Drupal is a powerful publishing and content management system. Users can add all sorts of content to Web pages through a system of modules. The software itself is free and open-source; users need simply pick out which site elements they want, and then put them together.
Drupal has been used on several popular and professional sites. One of the most notable is The Onion, the satirical news publication, as well as MTV's Web site in the United Kingdom. In its latest iteration, version 6, it has added support for drag-and-drop, OpenID logins, and an editor that can be tuned to suit both left, and right viewing cultures.
Winner: Drupal (Drupal.org)