ReactXP is an open-source cross-platform application framework for creating user interfaces and experiences. It acts as an extension of the React JavaScript library, allowing developers to create native applications on multiple platforms, including iOS, Android, and web, from a single codebase. ReactXP provides APIs that abstract platform-specific details, enabling efficient development across different environments. Its features include a concise syntax with reusable components, state change management without direct manipulation of DOM or UI elements, and automatic component updates upon data changes. ReactXP also supports styling through standard CSS rules and media queries that adapt the layout based on screen size or orientation; this simplifies the implementation of responsive design across all platforms.