- Yahoo! UI Library
- Prototype and Scriptaculous
- DoJo Toolkit
- Google WebToolkit
- and other smaller ones…
There is a big community behind JQuery that keeps the libraries uptodate and browser-conform and there is also a possibility to use jquery and MooTools or other js-libraries in combination / at the same time, namely by using the jquery compatibility mode by calling the method “
For PHP-coders I also recommend using the two libraries Scriptaculous (for effects) and Prototype (for the core), which are, by now, also part of Ruby on Rails Framework.
I also tried the Dojo Toolkit. In short, it is quity easy to use but much much too big, therefore using the default dojo library makes your site much slower, therefore I do not recommend using Dojo.
For more information about current developments on AJAX in web look at the Ajaxian.com with its resources page, that seem to be keeped up2date.
There is also an article about “2007 Ajax Tools Usage Survey Results“, where Prototype and JQuery were the most used libraries by end of the year 2007.