script.aculo.us provides you with easy-to-use, cross-browser user interface JavaScript libraries to make your web sites and web applications fly

jQuery is a new kind of JavaScript Library

Ext JS is a JavaScript platform for rapid development of cross-browser web apps

scripty2 is a powerful, flexible JavaScript framework

A lightweight Javascript library

MooTools is a compact, modular, Object-Oriented JavaScript framework designed for the intermediate to advanced JavaScript developer

YUI 3 is Yahoos next-generation JavaScript and CSS library

Prototype is a JavaScript Framework that aims to ease development of dynamic web applications

Javascript for rich internet applications

Ajax, events, packaging, CSS-based querying, animations, JSON, language utilities, and a lot more

The ultra lightweight JavaScript library

Raphaël is a small JavaScript library that should simplify your work with vector graphics on the web

A pure-JavaScript CSS selector engine designed to be easily dropped in to a host library