Flutter resources:

Wonderous (web demo, App Store, Google Play, source code):
A Flutter app that showcases Flutter’s support for elegant design and rich animations.
Material 3 Demo (web demo, source code):
A Flutter app that showcases Material 3 features in the Flutter Material library.
Flutter Samples (samples, source code):
A collection of open source samples that illustrate best practices for Flutter.
Widget catalogs (Material, Cupertino):
Catalogs for Material, Cupertino, and other widgets available for use in UI.