meSpeak.js : meSpeak.js (modulary enhanced speak.js) is a 100% client-side JavaScript text-to-speech library
Crafty : JavaScript Game Engine, HTML5 Game Engine
Bliss.js : Want to use Vanilla JS but find native APIs a bit unwieldy? Bliss is for you
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 ...
rsvp.js : A lightweight library that provides tools for organizing asynchronous code
Modest Maps is a small, extensible, and free library for designers and developers who want to use interactive maps in their own projects.