Dojo - JavaScript Ajax Library

Dojo is an Open Source DHTML toolkit written in JavaScript. It builds on several contributed code bases (nWidgets, Burstlib, f(m)), which is why we refer to it sometimes as a "unified" toolkit. Dojo aims to solve some long-standing historical problems with DHTML which prevented mass adoption of dynamic web application development.

Links
http://dojotoolkit.org/
http://dojo.jot.com/WikiHome
http://manual.dojotoolkit.org/WikiHome/