Xaraya is an elegant and extremely capable content management system coded in PHP and MySQL. In the standard form it includes a built-in forum, blog, articles with multiple content types, sophisticated handling of users / roles etc. - a very comprehensive package.
Furthermore everything including the standard features is modular and connects to other modules through pre-defined hooks. Many of the built-in modules can be extended to perform new tasks and completely new modules can also be built. It is, in effect, a very sophisticated framework for building web-based applications.
For more information please see the Xaraya web site.