Flutter is an open-source UI software development kit created by Google. It is used to develop applications for Android, iOS, Windows, Mac, Linux, Google Fuchsia and the web. Flutter apps are written in the Dart language. Flutter is Google’s UI toolkit for building beautiful, natively compiled applications for mobile, web, and desktop from a single codebase. Flutter code is compiled to native ARM machine code using Dart's native compilers. Thus Flutter gives you full native performance on both iOS and Android.
Best Flutter Alternatives
Create native apps for Android and iOS using React. React Native is an open-source mobile application framework created by Facebook.
Open source platform for building Android and iOS apps with .NET and C#. Build native Android, iOS, tvOS, watchOS, macOS, and Windows apps with .NET with native API access.
Ionic Framework is the free, open-source mobile UI toolkit for developing high-quality cross-platform apps for native iOS, Android