Some popular JavaScript frameworks

ASP.NET Ajax Framework http://asp.net/ajax
Clean Ajax Framework http://sourceforge.net/projects/clean-ajax
Dojo Toolkit http://dojotoolkit.org
jQuery http://jquery.com
MochiKit http://mochikit.com
MooTools http://mootools.net
OpenJS http://openjs.com
Prototype http://prototypejs.org
Rialto http://rialto.improve-technologies.com/wiki
script.aculo.us http://script.aculo.us
393Framework Web address
Spry Framework http://labs.adobe.com/technologies/spry
YUI http://developer.yahoo.com/yui