Google hosts all the popular ajax libraries on their servers so you don’t have to keep a copy on your own ajax enabled web site.

See http://code.google.com/apis/ajaxlibs/documentation/index.html for the following ajax Libraries:

• jQuery
• jQuery UI
• Prototype
• script_aculo_us
• MooTools
• Dojo
• SWFObjectNew!
• Yahoo! User Interface Library (YUI)New!
• Ext CoreNew!

This is a great service and if widely implemented should significantly speed your end user’s experience as well as reducing load on your own servers.