jQuery is a fast and concise JaScript Library that simplifies HTML document trersing, event handling, animating, and Ajax interactions for rapid web development. jQuery is designed to change the way that you write JaScript.

MooTools is a compact, modular, Object-Oriented JaScript framework designed for the intermediate to advanced JaScript developer. It allows you to write powerful, flexible, and cross-browser code with its elegant, well documented, and coherent API.

Ajax.org Platform is a pure jascript application framework for creating real-time collaborative applications that run in the browser.