Drupal

Drupal is a free software package that allows an individual or a community of users to easily publish, manage and organize a wide variety of content on a website. Tens of thousands of people and organizations have used Drupal to power scores of different web sites, including Community web portals, Discussion sites, Corporate web sites, and more!

Drupal is ready to go from the moment you download it. It even has an easy-to-use web installer! The built-in functionality, combined with dozens of freely available add-on modules, will enable features such as Content Management Systems, Blogs, and Collaborative authoring environments, and more!

Visit website for more information: http://www.drupal.org