Geeklog is an open source application for managing dynamic web content. It is written in PHP and supports MySQL, PostgreSQL, or MS SQL as the database backend.
"Out of the box", Geeklog is a CMS, or a blog engine with support for comments, trackbacks, multiple syndication formats, spam protection, and all the other vital features of such a system.
The core Geeklog distribution can easily be extended by the many community developed plugins and other add-ons to radically alter its functionality. Available plugins include forums, image galleries, and many more.
I code and work on some documentation for Geeklog. I've also participated in the Google Summer of Code through Geeklog as both a mentor and an admin.