Crafty : JavaScript Game Engine, HTML5 Game Engine
Zepto.js : Zepto is a minimalist JavaScript library for modern browsers with a largely jQuery-compatible API. If you use jQuery, you already know how to use Zept...
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 ...
Wave.js : Audio visualizer library for javascript. Create dynamic animations that react to an audio file or audio stream.
Tracery : A story-grammar generation library for javascript. Write grammar objects, get generative stories.
Modest Maps is a small, extensible, and free library for designers and developers who want to use interactive maps in their own projects.