As reported in this new post on our sister site, AjaxDeveloper today, there's a new release - the CBL Partial Updater PHP & Ajax library.

CBL Partial Updater is an AJAX library for PHP. Unlike other libraries, all operations are controlled at the server side. Using the library, existing PHP scripts can be converted to AJAX in less than a minute.

In 2005/09/22 release, added support for spinners (loading indicators).

I'll have to check out the "existing PHP scripts can be converted" aspect of it to see how it handles. It's nice that it's so tied in with the backend like that, but I wonder if that's a trade-off for something more portable...