http://backbonejs.org/#introduction
Backbone.js gives structure to web 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 API 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, a list of tutorials and a long list of real-world projects that use Backbone. Backbone is available for use under the MIT software license.
You can report bugs and discuss features on the GitHub issues page, on Freenode IRC in the #documentcloud channel, post questions to the Google Group, add pages to the wiki or send tweets to @documentcloud.
Backbone is an open-source component of DocumentCloud.