jquip : Smaller, Lighter, Faster, more modular jQuery - include only the parts you want! Don't use it, Don't include it.
meSpeak.js : meSpeak.js (modulary enhanced speak.js) is a 100% client-side JavaScript text-to-speech library
Ember.js : A JavaScript framework for creating ambitious web applications
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.
Band.js : An interface for the Web Audio API that supports rhythms, multiple instruments, repeating sections, and complex time signatures.
Sammy is a tiny javascript framework built on top of jQuery, It's RESTful Evented Javascript.