Flutter is a powerful open-source UI framework developed by Google for creating visually appealing, natively compiled applications across multiple platforms, including iOS, Android, web, macOS, Windows, and Linux, from a single codebase. With its expressive and flexible UI components, Flutter allows developers to build custom interfaces quickly and efficiently. The framework also boasts a rich set of pre-designed widgets, seamless integration with various tools, and a strong developer community, making it a top choice for cross-platform development.