Drupal (pronounced /ˈdruːpəl/) is a free and open source content management system (CMS) written in PHP and distributed under the GNU General Public License.[2][3][4] It is used as a back-end system for at least 1% of all websites worldwide ranging from personal blogs to larger corporate and political sites including whitehouse.gov and data.gov.uk.[5][6] It is also used for knowledge management and business collaboration.