Drupal is an open-source content management system (CMS) that was originally created as an internal message board. It allows users to publish and organize content and can be configured for different uses from personal blogs to large community sites. Drupal uses a plugin architecture that supports community building through modules for forums, messaging, events, and member attribution. As a web 2.0 platform, Drupal emphasizes participation, harnessing collective knowledge, and network effects through features like content syndication.