One of the best content management system i’ve used so far is Drupal. This is top notch open source software program, and is widely popular system for putting communities online. Drupal supports a wide variety of features, from basic content uploading, to support for user profiles, chatting, tagging, and voting. Drupal recently launched their 6.0 version, they have added more usability improvements and some bug fixes. One of my favorite features is the built in multisite capability. I have clients running several sites sharing the same code base, one even shares the same database between the sites. Check out this cool open source cms today!