Published on 2007-02-09 by John Collins. Please follow me on Twitter for more: 

I've been browsing through the Javascript widget library provided freely by Yahoo!, there are some nice examples here showing off some of the features on offer:

Yahoo! UI Library (YUI)

A few years back this would have been called a DHTML library, but somehow that term has fallen out of fashion despite the underlying technologies being the same, that's the marketing of technology for you ;-)