(http://dart-lang.github.io/widget.dart/, developed by Kevin Moore.)

The Dart widgets project by Kevin Moore builds on the Dart web UI and gives us a collection of reusable components and effects. It is a port to Dart's Web UI library from the widely successful Twitter Bootstrap project (http://twitter.github.io/bootstrap/), which helps web developers build responsive designs for web apps. This means dynamic widgets, such as accordion, alert, carousel, collapse, dropdown, tabs, and more, are reborn as actual web components. To see all of them in action, please refer to http://dart-lang.github.io/widget.dart/, where you can find more documentation and examples. The code can be found at https://github.com/dart-lang/widget.dart.

This project can also be a source of inspiration for building your own Polymer components.