Expo is an open-source platform that provides a comprehensive ecosystem of tools for developers to create, build, and deploy native applications across Android, iOS, and the web using a single React codebase. With over 900,000 projects and a significant portion of React Native projects utilizing Expo, it offers services like app store submission, over-the-air updates, and a community-driven support system. Expo differentiates itself by simplifying the development process, allowing for rapid iteration and deployment, making it a go-to solution for mobile app developers.