Today I present interesting AJAX-library YUI (http://developer.yahoo.com/yui/). It developed by Yahoo internet search system.
YUI has nice license - BSD License (http://developer.yahoo.com/yui/license.html).
Last library version (2009/08) - 2.7.0
YUI has maximal full documentation (API documentation, examples gallery, YUI Theater - video, Cheat Sheets).
You need have Firefox with Firebug (look at Firefox additions or http://getfirebug.com/).
Main library features will be discussed in next posts.