For those of you that don’t know, Yahoo has a set of open source utilities written in JavaScript. It includes some helpful tools for DOM scripting, DHTML and AJAX. Many of these tools are used in their applications and are available through their developer network.
This is the second release I believe and it includes some useful everyday tools that people are interested in using. Some of the utilities include event handling, animation, and drag and drop. Also part of their library controls are auto complete, a calendar, menus, and a tree view.
Many of these utilities can be implemented in your everyday web applications and since its open source all of these can be manipulated to suit the needs of your project. I know many people have checked this page out. Let me know if you have had any success in using some of the Yahoo UI Library.