After years in development I've finally released my content management system, Gatherer, on Google Code.  GCMS is written in PHP using the Zend Framework and Smarty.  It is a fully featured "Web 2.0" CMS with WYSIWYG editors, syndicate support, and AJAX.  You are currently seeing GCMS in action right now and if you'd like to give it a try on your site check out the link in the menu or go to the Google Code site.