Joining Cybozu Labs, I started looking at AJAX. However, the existing libraries that I found all seemed to me a bit too complicated. So I decided to write my own; CBL Partial Updater, that focuses on conversion of current PHP scripts to AJAX apps.
CBL Partial Updater is an AJAX library for PHP. Unlike other libraries, all operations are controlled at the server side. Using the library, it is very easy to add AJAX features to existing PHP applications.
Just add a few lines to your PHP and HTML, and your web application turns into an AJAX app.
An example is located here. As you can see, existing PHP scripts can be converted into AJAX apps in less than a minute.
2005/09/22: For latest information, please see the category page of CBL Partial Updater.