Project Engineering Intern at Mariana Minerals | San Francisco

About CluelyAt Cluely, we are revolutionizing the way people interact with AI by providing unparalleled advantages in diverse situations. Our innovative desktop assistant leverages screen, microphone, and audio context to deliver insights and suggestions that traditional models fail to offer due to contextual limitations.Our success hinges on two key factors:1) Chatbots are not the ideal interface for multi-modal AI.2) We possess the ability to make anything go viral.About the RoleAs an Engineering Intern at Cluely, you will be immersed in a dynamic environment where our engineering team works six days a week in-person in San Francisco, dedicating 10-12 hours each day. We provide housing within a block of the office to ensure your convenience and focus.Our engineering team comprises both seasoned professionals and ambitious young talent, creating a unique blend of skills and creativity. For more insights into our team, check out this link.Ideal Candidate ProfileYou are among the top engineers globally.You are willing to invest your life in the pursuit of greatness.

At Cluely, we excel in crafting exceptional videos, an integral part of our innovative approach to storytelling.We are on the lookout for talented individuals who are passionate about elevating our video production quality. If you possess a deep understanding of cinematography, lighting, directing, and have a rich history of creating films or short content, this is a role for you!A sense of humor is a must! A significant aspect of our selection process involves assessing your ability to produce entertaining content that brings smiles and laughter.As a versatile generalist, you will often operate independently, managing all aspects of production. Whether you want to create a podcast or a video segment, you will be responsible for conceptualizing the scenes, sourcing props, setting up lighting, and acquiring equipment.This position requires a commitment of 12 hours a day, six days a week. Expect an intense yet rewarding experience working alongside a young, dynamic team just a block away from our office.In return for your dedication, we offer:A competitive salary ranging from $150K to $200K, along with equityComplimentary housingFree mealsAn opportunity to work in a fast-paced early-stage tech startup environmentConnections with influential figures in the industryA chance for a guaranteed relationship after one year

About TacitTacit is a pioneering deep tech startup located in San Francisco, focused on creating groundbreaking hardware that transforms human-computer interaction. Supported by notable investors such as General Catalyst, Khosla Ventures, and Greylock Partners, our founding team comprises experts from Stanford, BrainGate, Oculus, and Tesla. While we are unable to disclose extensive details at this moment, our team is passionately addressing advanced engineering challenges to develop revolutionary products.About the RoleWe are on the lookout for a driven Electrical Engineering Intern to assist in the development and scaling of test infrastructure for our innovative sensing technology. This internship will provide you with hands-on experience across hardware, firmware, and automation systems, emphasizing the enhancement of test coverage and product reliability. You will have the opportunity to engage in collaborative learning and actively participate in product development within a vibrant startup atmosphere.What You'll DoAutomate lab equipment and validation workflowsDesign and construct custom PCBs for test jigsContribute to embedded firmware to support test hooks and diagnosticsDevelop a continuous integration (CI) test rack to automatically validate firmware releases and sensor performanceAssist in sensor characterization and calibration to minimize device-to-device variabilityDocument and effectively communicate engineering findings and recommendations.Ideal Candidates May HaveProficiency in Python, PCB Design (Altium), Embedded C/C++A strong independent work ethic, adaptability, and resourcefulness.Excellent communication and teamwork abilities.Comfort in a fast-paced startup environment, with a passion for independent building.CompensationHourly rate determined by your individual skills and experience.

About RoamRoam is an innovative Applied AI lab dedicated to the development of World Models for immersive 3D environments. We are pioneering the transition from traditional 2D pixel representations to fully interactive 3D worlds. Our initiatives encompass everything necessary for perception, reasoning, and creation within 3D spaces, with diverse applications in simulation, design, and gaming.Our primary focus is the gaming sector, where we specialize in 3D environment generation and understanding for interactive entertainment. Our cutting-edge technology empowers millions of users to create, explore, and share captivating worlds together.Much like TikTok democratized content creation, our mission is to enable everyone to transform their ideas into games without requiring any technical expertise.Since our inception earlier this year, we have achieved remarkable milestones:Onboarded over 1,000 gaming and livestream creators (each with 100K–10M followers) ready to launch Roam games, collectively reaching an audience of over 250 million fans.Assembled a dynamic team of 12 applied AI experts from leading organizations like ByteDance Seed, Nous Research, OpenCSG, and NASA, including seasoned technical founders and engineers who have successfully launched over 100 games.Secured investment from notable backers including Google DeepMind, ByteDance, Anduril, Together AI, and Polymarket, alongside prominent founders and content creators.Acquired a consumer product studio boasting over 11.5 million downloads.About the Role:In this role, you will delve into the intersection of applied AI and large-scale systems, concentrating on world generation pipelines, data-efficient training methodologies, and real-time optimization techniques. Your contributions will empower users to create, engage with, and monetize immersive games and 3D environments. Key responsibilities include:Designing and implementing game generation pipelines utilizing LLMs and advanced agentic chains.Enhancing game iteration cycles, model accuracy, and generation speed across mobile and cloud infrastructures.Scaling the product effectively.Establishing feedback loops that learn from player interactions and self-play to automatically test and enhance games in real-time.Delivering context-aware creation through multi-turn dialogues and granular parameter control.

Sieve is an AI research lab based in San Francisco, focused on large-scale video data. The team builds and maintains infrastructure capable of handling exabyte-scale video, while developing advanced methods for video understanding. Sieve also curates extensive and diverse datasets to support new approaches in video modeling. With video now accounting for a significant portion of internet traffic, the company aims to remove barriers to high-quality training data for fields like creativity, communication, gaming, AR/VR, and robotics. The company recently completed its Series A and is backed by investors including Matrix Partners, Swift Ventures, Y Combinator, and AI Grant. Sieve has worked with leading AI labs and continues to grow, generating $XXM last quarter with a small team of 15. Role overview The Software Engineering Intern at Sieve works across the stack to help build and scale data pipelines that deliver video datasets to clients. This role involves taking full ownership of projects, from sourcing and curating video data to developing machine learning filters, improving system efficiency, and building internal dashboards for quality assurance and delivery. The work directly impacts the timely delivery of high-quality data to customers. What you will do Build and scale data pipelines for delivering video datasets Source and curate video data for a range of applications Develop and refine machine learning filters to enhance data quality Improve system efficiency and reliability Create internal dashboards for quality assurance and delivery tracking Who thrives here This internship is well suited to those who enjoy solving complex technical problems, want to collaborate directly with customers at the forefront of Video AI, and seek meaningful challenges in a high-performance setting.

Netic stands at the forefront of artificial intelligence innovations, empowering essential services that serve as the backbone of the American economy.With an impressive $43 million in funding from renowned investors such as Founders Fund, Greylock, Hanabi, and Dylan Field, who spearheaded our Series B, we've enabled our clients to secure numerous jobs across various service industries in North America. Today, there are businesses that operate solely on an AI-first approach using Netic.Join our dynamic team comprised of relentless builders from top companies like Scale, Databricks, HRT, Meta, along with graduates from prestigious institutions like MIT, Stanford, and Harvard, as we integrate frontier AI into the physical economy, tackling complex challenges with immediate and tangible impacts.At Netic, we create features that empower businesses through AI. As an intern, you will receive dedicated mentorship guiding you through the entire process of supporting customers, launching features, and iterating swiftly.This internship spans 12 weeks and is set to commence in the Summer of 2026 or earlier.

About CartesiaAt Cartesia, we are on a mission to revolutionize AI by creating interactive intelligence that seamlessly operates across all environments. Our innovative approach aims to enable continuous processing and reasoning over extensive streams of audio, video, and text data, paving the way for on-device capabilities that were previously unimaginable.Founded by PhDs from the Stanford AI Lab, our team has pioneered State Space Models (SSMs) — a groundbreaking method for training efficient, large-scale foundation models. We blend profound expertise in model innovation and systems engineering with a design-oriented product engineering ethos, allowing us to develop and launch advanced models and user experiences.Supported by top-tier investors such as Index Ventures and Lightspeed Venture Partners, along with a network of esteemed advisors and over 90 angel investors, we are well-positioned to lead the charge in AI development.About the RoleAs part of our early talent program, Cartesia is seeking a Product Engineer Intern who will play a pivotal role in delivering impactful, model-driven experiences across our platforms, including our marketing site, onboarding processes, self-serve funnels, dashboards, documentation, and APIs. You will collaborate closely with our go-to-market, model serving, research, and product teams.In this internship, you will engage in end-to-end development, iterating and measuring developer-centric product experiences that enhance activation, retention, and revenue. Your contributions will be integral to our production processes, allowing you to own significant portions of the product and witness your efforts directly influencing Cartesia's growth.Your ImpactDesign and implement growth-oriented surfaces for developers by leveraging user insights, data, and fundamental principles.Accelerate the market introduction of Cartesia’s latest models through the rapid development of high-performance interfaces and user flows.Track and analyze crucial performance metrics (e.g., user sign-up to first call, time-to-first-production-use, feature adoption) and iteratively improve based on actual user interactions.Publicly communicate your work via Cartesia’s official channels as well as your own professional profiles.Engage in cross-functional collaboration with various teams to create solutions that expand Cartesia's reach and enhance our collective work.Identify and alleviate pain points throughout the user journey, from initial engagement to product utilization.

About Mariana Minerals Mariana Minerals is a software-focused minerals company based in San Francisco. The team delivers essential minerals that support energy, artificial intelligence, and defense technologies. By combining industry expertise with advanced software, automation, and data-driven methods, Mariana Minerals aims to transform the minerals supply chain. Mechanical Engineering Intern – Role Overview The Mechanical Engineering Intern will join the Pilot Plant Operations team at the San Francisco headquarters. This role centers on hands-on work: designing, improving, and optimizing benchtop pilot plant equipment. Interns collaborate with seasoned engineers and domain experts, gaining practical experience that goes well beyond typical support tasks. What You Will Do Create 3D models, layout drawings, and technical documentation for laboratory and pilot plant equipment. Build, test, and refine mechanical solutions to improve equipment performance, reduce downtime, control costs, and support health and safety. Work with engineering, management, and software teams to develop programs and applications that advance Mariana Minerals’ operations. Partner with colleagues from engineering, operations, and controls engineering to reach project objectives. Share your findings and experiences in a final presentation at the end of the internship. Desired Qualifications Currently enrolled in or recently graduated from a mechanical engineering or related degree program. Solid grasp of mechanical design documentation, including equipment specifications, layout drawings, piping diagrams, and CAD models. Hands-on experience designing or supporting industrial equipment such as pumps, piping systems, reactors, separators, filtration systems, or material handling equipment. Ability to design mechanical solutions independently, troubleshoot issues, and analyze complex data sets. Strong technical writing, communication, and teamwork skills. Comfortable adapting to changing priorities and managing multiple tasks in a busy environment. Why Mariana Minerals? Interns at Mariana Minerals join a mission-driven group focused on reshaping the future of critical minerals supply.

About Mariana Minerals Mariana Minerals is a software-driven minerals company based in San Francisco. The team supplies essential minerals for the energy, artificial intelligence, and defense industries. By combining deep industry knowledge with advanced software, automation, and data strategies, Mariana Minerals is rethinking how minerals reach the world’s most critical sectors. Internship Overview The Process Engineering Intern will join the Pilot Plant Operations team at Mariana Minerals’ San Francisco headquarters. This internship offers the chance to work on meaningful, hands-on projects in mineral processing. Interns conduct benchtop experiments, support pilot plant test runs, and help develop new operational programs. Close collaboration with experienced engineers and subject matter experts is a core part of the experience. This role focuses on building and delivering new solutions, not just supporting existing work. What You Will Do Run experiments in both lab and pilot plant settings to help reduce risks in scaling up minerals processing. Develop, test, and refine approaches to improve product recovery, minimize equipment downtime, control costs, and support health and safety. Work with engineering, management, and software teams to create programs and tools that advance operational goals. Collaborate with cross-functional groups, including operations and analytical labs. Present findings and insights at the end of the internship. What We’re Looking For Current student or recent graduate in chemical engineering, metallurgy, materials science, or a related field. Strong grasp of process design, thermodynamics, and reaction engineering. Hands-on experience in laboratory, pilot plant, or commercial plant settings through coursework, projects, or previous internships. Skilled in experimental design, troubleshooting, and independent analysis of complex data. Clear technical writing, communication, and collaboration abilities. Comfortable adapting to new challenges and working in a changing environment. Why Mariana Minerals? Interns at Mariana Minerals join a mission-driven team working to transform the global sourcing and supply of critical minerals. Every contribution supports a larger vision for the future of the industry.

This position offers flexibility for both Remote (US) and in-person roles based in San Francisco, CA.About OliveAt Olive, we’re revolutionizing how companies develop internal tools by enabling them to articulate their needs using natural language.From dynamic sales dashboards to comprehensive trust & safety workflows, internal tools serve as the operational backbone for today’s enterprises. However, creating these tools has traditionally been a slow and tedious process that drains engineering resources.Olive changes the game by transforming simple prompts into fully functional, full-stack internal tools connected to organizational data in mere minutes. Our innovative platform harnesses the power of large language models (LLMs) and advanced code generation techniques to deliver production-ready tools that provide unprecedented insights and operational efficiency.With a successful $2.1M seed funding round from top-tier investors and angel backers, we are on an exciting trajectory to scale our talented team.This role presents an exceptional opportunity to contribute to a challenging yet impactful project, characterized by speed and a strong focus on delivering results. If this sounds exciting to you, we encourage you to apply.The RoleWe are seeking a highly motivated Software Engineering Intern to join our team for the upcoming summer (or fall/spring semester). You will collaborate closely with our founders, engage across the tech stack, and explore the boundaries of robust full-stack software development leveraging AI. This is a paid internship.In this role, you will play a critical part in building on our LLMs and agentic workflows to facilitate code generation, deployment, and tool utilization for enterprise applications. By the end of the internship, you will have developed significant features and functionality that will make a tangible difference.Our team is vibrant, hardworking, and supportive, always prioritizing the customer experience to craft delightful product interactions.

Join our dynamic core engineering team at AfterQuery, where you'll play a pivotal role in developing cutting-edge data infrastructure that will influence the advancement of frontier AI models. This position offers substantial responsibility, allowing you to oversee entire projects from inception to completion—providing immediate visibility of your contributions.Company OverviewAfterQuery is an innovative research lab at the forefront of artificial intelligence, exploring its limits and potential through unique datasets and experiments. Our primary clientele consists of foundation model labs, making us a vital partner for leading AI research labs worldwide.Headquartered in San Francisco, CA, we have garnered support from top-tier investors including Y Combinator, BoxGroup, and former partners from Lightspeed and Index Ventures, as well as prominent figures from Google DeepMind and Meta GenAI.Our founding team is composed of experts from prestigious organizations such as Jane Street, Meta, Citadel Securities, Google, Goldman Sachs, Morgan Stanley, Silver Lake, and leading AI research institutions like Berkeley AI Research (BAIR) and Stanford AI Laboratory (SAIL).Why You Should ApplySignificant Growth Potential: As one of the fastest-growing YC companies, we are poised to set records in our sector.Founding Role: Take charge of our data infrastructure from day one and leave your mark.Exceptional Team: Collaborate with a founding team that boasts experience from top firms like Citadel Securities, Meta, and Google.Key ResponsibilitiesDesign and implement complex data capturing workflows across web (Next.js) and desktop (Python) environments.Architect and enhance data pipelines to handle high throughput and heavy loads efficiently.Work closely with the founding team to shape product strategy and rapidly deploy features.Establish engineering best practices and prepare for future team expansion.Essential QualificationsMust be able to take a gap semester and work on-site in San Francisco.Proficient in JavaScript (Next.js) and Python, with a proven track record of developing full-stack web applications.Experience with serverless architecture and cloud services (GCP/AWS) for intensive data processing.Familiarity with caching (Redis), indexing (Elasticsearch), and message queues (Kafka) is a plus.

About DittoDitto is revolutionizing social connections on college campuses as a leading dating platform. In just three months, we've expanded our user base threefold to over 120,000, backed by a $9.2 million seed round from top-tier investors including Google and prominent venture capital firms. Our mission is to create a product that fosters genuine matchmaking for Gen Z, and we’re only at the beginning of our journey.About the RoleJoin us as we craft an innovative social network powered by AI, where intelligent agents do more than assist — they enhance the entire user experience. We're in search of a passionate Product Engineer Intern who has experience launching consumer products that resonate with users. In this role, you will be responsible for developing user-facing experiences from conception to execution, ensuring they are engaging and seamlessly integrated.Your contributions will be vital in realizing Ditto's matchmaking and engagement engine, bringing to life the experiences that captivate our users while building the infrastructure that makes these interactions feel extraordinary. You will work closely with product managers, researchers, and infrastructure teams to define and refine the core elements of Ditto's platform.In This Role, You WillManage complete product experiences across matching, chat, scheduling, and user re-engagement — from ideation to launch and beyond.Make daily product decisions regarding development priorities, user experience, release timelines, and performance metrics.Design and implement AI-driven product flows where intelligent agents execute tasks while you focus on enhancing the user experience.Develop AI-orchestrated pipelines that automate workflows, replacing manual processes with streamlined solutions.Create internal tools allowing both humans and AI to assess system performance, debug agent activities, evaluate results, and guide system development.Establish feedback mechanisms linking user interactions, agent decisions, and real-world outcomes, including matches, responses, dates, and user retention.Rapidly prototype and iterate based on actual user data, fostering a culture of data-driven decision-making.How You Will WorkYou will function as a product-oriented manager of AI systems. Your role is not solely about coding; it’s about orchestrating the overall user experience through strategic oversight and innovative thinking.

About TacitTacit is an innovative deep tech startup located in the heart of San Francisco, pioneering hardware solutions that redefine human-computer interaction. Supported by prominent investors such as General Catalyst, Khosla Ventures, and Greylock Partners, our founding team comprises experts from esteemed organizations like Stanford, BrainGate, Oculus, and Tesla. While our groundbreaking products are still under wraps, our team is dedicated to tackling formidable engineering challenges to revolutionize the tech landscape.About the RoleWe are looking for an enthusiastic Software Engineering Intern to contribute to the development of the next generation of human-computer interfaces. This internship offers invaluable hands-on experience in both front-end and back-end development, focusing on creating user-centric applications and aiding internal research processes. You will collaborate closely with a talented team of engineers, designers, and researchers to bring innovative interaction paradigms to fruition.Key ResponsibilitiesDesign and implement applications for web, mobile, and embedded clients that interface with our hardware.Build backend services for real-time interaction and seamless data streaming.Develop internal tools for data labeling, visualization, and debugging purposes.Rapidly prototype new user experiences utilizing novel input methods.Collaborate with full-time engineers to deploy stable, high-performance software solutions.Document engineering insights and articulate design decisions effectively.Preferred QualificationsProficiency in Python, TypeScript, React, Linux, and command-line development.Demonstrated ability to work independently, with a strong sense of flexibility and resourcefulness.Excellent communication and teamwork skills.Ability to thrive in a fast-paced startup environment, with a keen interest in independent project development.CompensationHourly compensation will be determined based on your individual skills and experience.

Join Dryft as a Full-Stack Engineering Intern!About Us: At Dryft, we develop advanced systems designed to streamline intricate human decision-making processes in manufacturing operations. Our compact yet highly skilled team is deeply rooted in a passion for the tangible world, embracing everything from cars and machines to aircraft. Our diverse group includes alumni from prestigious universities such as Stanford, Berkeley, MIT, and TUM, and boasts accolades from events like Stanford TreeHacks. We have engineered everything from robots and race cars to software with millions of downloads.Backed by visionaries from Amazon, Facebook, Stripe, Applied Intuition, and supported by investors like General Catalyst and Neo, our team is committed to innovation in industrial technology.At Dryft, we foster a culture of straightforward communication and direct feedback. We seek individuals who aspire to grow rapidly while taking on significant responsibilities.Your Role:As a Full-Stack Engineering Intern, you will play a crucial role in shaping Dryft's decision intelligence framework. You will design scalable systems that integrate agent-based reasoning, mathematical optimization, and simulations utilizing vast industrial datasets.This position allows you to work independently on dedicated projects, often collaborating directly with customers while receiving mentorship from experienced engineers who will guide you throughout your journey. Many of our foundational engineers have previously been integral members of venture-backed startups in the San Francisco area.Qualifications:You are passionate about creating scalable, interpretable, data-driven agents from multiple angles including algorithms, architecture, and infrastructure.You possess a keen product sense and thrive in direct daily interactions with customers.You have successfully shipped production code end-to-end, demonstrating strength in backend and infrastructure, while being comfortable implementing fundamental frontend features.You are prepared to work onsite in San Francisco (visa support is available).

Join Strava: Where Active Lives ThriveStrava is the premier application for active individuals, boasting a vibrant community of over 180 million athletes across more than 185 countries. It's not just about tracking workouts; it's about fostering progress and achieving personal milestones together. Whether you enjoy running, cycling, swimming, or any other sport, Strava is your partner in success. Connect with others, surpass your goals, and ensure that every effort counts. Embark on your journey with Strava today.Our mission is straightforward: to inspire individuals to lead their most active and fulfilling lives. We firmly believe in the transformative power of movement to unite and propel people forward.As part of the Foundation engineering team at Strava, you will play a critical role in maintaining the infrastructure that supports millions of athletes worldwide. We design and refine tools and systems that empower our developers, sales, and support teams to deliver features with confidence, safety, and efficiency. In your role as a Senior Engineer, you will be instrumental in shaping and enhancing Strava’s internal platform and administrative tools. This is your chance to significantly impact by modernizing internal tools for customer support teams, enhancing their productivity and their ability to deliver outstanding athlete experiences.We embrace a hybrid work model, allowing you to spend more than half your time on-site at our San Francisco office — three days each week.

Join the Delphi Team!At Delphi, we are revolutionizing knowledge sharing through the creation of interactive digital minds that engage in meaningful conversations, provide learning opportunities, and offer guidance.Unlike traditional static profiles and endless feeds, Delphi presents a dynamic, interactive identity layer that embodies your voice, perspectives, and insights. This allows others to experience your thought process rather than just reading about it.We are committed to making Delphi accessible to everyone, enabling anyone to establish a digital mind as a constant presence that can respond to inquiries on your behalf.Our mission is ambitious:To make human wisdom abundant, personalized, and easy to discover.To preserve legacies, unveil opportunities, and amplify brilliance across generations.To ensure Delphi serves as everyone’s living profile that showcases their knowledge.We are proud to be trusted and appreciated by some of the brightest minds globally, from Simon Sinek to Arnold Schwarzenegger (interact with them here). Our growth has been remarkable, tripling our revenue, user base, and interactions in the last six months solely through word-of-mouth. We are poised to accelerate further.Our investors include prominent names like Sequoia Capital, Founders Fund, Abstract Ventures, and many founders from successful companies such as Lyft, Zoom, and DoorDash. Our team comprises successful founders and builders from industry giants like Apple, Spotify, and Substack.Discover more about Delphi and this role by connecting with the CEO's digital mind here

Composio develops communication infrastructure that helps agents connect with essential tools such as GitHub, Gmail, Notion, and Salesforce. The engineering team addresses challenges related to context and search, aiming to make these integrations more accessible and useful for agents. The company recently closed a $25 million Series A led by Lightspeed, with additional backing from Guillermo Rauch (CEO of Vercel) and Dharmesh Shah (CTO of HubSpot). Composio has tripled its annual recurring revenue this year, serving clients that range from Y Combinator alumni to established businesses like Wabi, Glean, and Zoom. Role overview This full-stack internship is based in San Francisco. Interns contribute to both developer and consumer web interfaces, supporting the Composio platform and its users. What you will do Enhance the user experience for teams using Composio by working on both the Composio Platform and Composio For You web interfaces. Design and implement clean, effective interfaces for frontend and SDK projects. Collaborate directly with customers to build relationships and gather feedback for product improvements. Write clear documentation to support both users and developers.

Role overview The City and County of San Francisco seeks a Stationary Engineer to help maintain and operate mechanical systems at San Francisco International Airport. This position centers on supporting sewage treatment operations, playing a key part in upholding the airport’s environmental standards and public health commitments. Main responsibilities Operate and monitor machinery and equipment involved in sewage treatment processes. Carry out routine maintenance and repairs to ensure efficient system performance. Respond promptly to alarms and emergency situations as needed. Maintain accurate logs and reports documenting daily activities and operations.

Join our dynamic marketing team at finvest as a Marketing Intern in San Francisco! This exciting summer internship offers you the chance to contribute to our growth strategies and enhance brand visibility in the fintech sector.The role has the potential to evolve into a full-time position based on performance and organizational needs.Your ResponsibilitiesAs an enthusiastic learner, you will engage in various marketing initiatives, including but not limited to:Creating and managing content for social media platformsAnalyzing marketing campaigns and deriving actionable insightsAssisting in the production of marketing materials and assetsContributing to brainstorming sessions for innovative marketing projectsConducting research on industry trends and competitor activities