Dojo is an Open Source DHTML toolkit written in JavaScript. Dojo allows you to easily build dynamic capabilities into web pages and any other environment that supports JavaScript sanely. With Dojo you can build degradable user interfaces more easily, prototype interactive widgets quickly, and animate transitions. Dojo’s event system, I/O APIs, and generic language enhancement form the basis of a powerful programming environment. When you write scripts with Dojo, you can include as little or as much of the available APIs as you need to suit your needs.

Requirements: Safari 2.0.x, Opera 9.0+, Internet Explorer 6+, Firefox 1+, Konqueror 3.5+
Demo: http://dojotoolkit.org/demos
License: Academic Free License, BSD License