Backbone.js is a lightweight JavaScript library that provides 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.
CodePlex is a Microsoft-hosted open source project hosting site. It provides a platform for developers to share and collaborate on code, manage and track work items, and access a wide range of tools to help build and maintain their projects.