clipboard.js : Copy text to the clipboard shouldn't be hard. It shouldn't require dozens of steps to configure or hundreds of KBs to load. But most of all, it should...
howler.js : howler.js is an audio library for the modern web. It defaults to Web Audio API and falls back to HTML5 Audio.
hunt : Library to detect when DOM elements become visible and disappear on scroll.
yepnope.js : A Conditional Loader For Your Polyfills!
Crafty : JavaScript Game Engine, HTML5 Game Engine
Rainbow is a code syntax highlighting library written in Javascript.
It was designed to be lightweight (1.4kb), easy to use, and extendable.
It is completely themable via CSS.