Drupal is a free & open source content management System (CMS) written in PHP & distributed under the GNU License. Used as a back end system for at least 1.9% of all websites worldwide used in personal blogs, political, corporate & government sites including NASA, whitehouse.gov, & data.gov.uk.
The standard release of Drupal core, contains basic features common with CMS. These include user account maintenance, registration, RSS feeds, menu management, system admin & page layout customization. The Drupal core installation can be used as a single- or multi-user blog, a brochure-ware website, a community or an Internet forum website with user generated content. Adding modules for flexabilty allows users to build a powerful web application.