The Yahoo! User Interface (YUI) Library is a set of utilities and controls, written in JavaScript, for building richly interactive web applications using techniques such as DOM scripting, DHTML and AJAX. The YUI Library also includes several core CSS resources. All components in the YUI Library have been released as open source under a BSD license and are free for all uses.
http://developer.yahoo.com/yui/
DefineItFast is primarily an online dictionary but not your typical web-based dictionary. It uses AJAX to make the search for definitions both fast and interactive. There aren’t many online dictionaries that offer similar live-search experience.
http://www.defineitfast.com