TodoMVC : A project which offers the same Todo application implemented using MV concepts in most of the popular JavaScript MV frameworks of today.
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 ...
xui.js : A super micro tiny DOM library for authoring HTML5 mobile web applications.
Bliss.js : Want to use Vanilla JS but find native APIs a bit unwieldy? Bliss is for you
Ember.js : A JavaScript framework for creating ambitious web applications
base2 is a lightweight library that irons out all the annoying differences in JavaScript implementations. It provides the additional functionality from JavaScript 1.6+ that only Mozilla browsers implement.