Backbone.js
►http://documentcloud.github.com/backbone/#
Backbone supplies structure to JavaScript-heavy applications by providing models with key-value binding and custom events, collections with a rich API of enumerable functions, views with declarative event handling, and connects it all to your existing application over a RESTful JSON interface.
The project is hosted on GitHub, and the annotated source code is available, as well as an online test suite, an example application and a list of tutorials.