MODx

MODx is a free, open source content management system and web application framework can handle high-volume sites, and offers the ability to handle multiple sites and subdomains from one install. "With Revolution you'll leverage the best things to come around since MVC and Active Record."

License: GPL
Written in: PHP
Operating system: Cross-platform

Website: http://modxcms.com/
Download: http://modxcms.com/download/
Documents: http://modxcms.com/learn/