Drupal is an open source content management platform. It is a community supported CMS that can be customized with PHP and expanded through modules. It powers over 450,000 sites and some well-known sites use it, such as Tim Berners-Lee's weblog. The basic concepts in Drupal include nodes, which are the fundamental building blocks, blocks which place items in regions, and users which can be assigned roles to control permissions. Functionality is expanded through modules and themes control the look.