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