TodoMVC : A project which offers the same Todo application implemented using MV concepts in most of the popular JavaScript MV frameworks of today.
script.aculo.us : script.aculo.us provides you with
easy-to-use, cross-browser user
interface JavaScript libraries to make
your web sites and web applications fly.
RequireJS : RequireJS is a JavaScript file and module loader. It is optimized for in-browser use, but it can be used in other JavaScript environments, like Rhino ...
React : A JavaScript library for building user interfaces
Band.js : An interface for the Web Audio API that supports rhythms, multiple instruments, repeating sections, and complex time signatures.
A library to generate PDFs in client-side JavaScript.