Flutter is an open-source UI software development toolkit created by Google for building natively compiled applications for mobile (iOS, Android), web, desktop, and even embedded devices — all from a single codebase.
Key Features of Flutter:
Cross-platform: Write one codebase and deploy it on multiple platforms.
Fast Development: Features like Hot Reload let you see changes in real-time.
Beautiful UIs: Comes with a rich set of pre-designed widgets that follow Material Design (Android look) and Cupertino (iOS look).

Dart Language: Flutter apps are written in Dart, a language also developed by Google.
High Performance: Compiles to native machine code using Dart's ahead-of-time (AOT) compilation.