Drupal

Drupal is a free and open-source content-management framework (CMS) written in PHP and distributed under the GNU General Public License. It is used as a back-end framework for at least 2.1% of all Web sites worldwide ranging from personal blogs to corporate, political, and government sites including WhiteHouse.gov and data.gov.uk. It is also used for knowledge management and business collaboration.

As of February 2014, there are more than 30,000 free community-contributed addons, known as contributed modules, available to alter and extend Drupal's core capabilities and add new features or customize Drupal's behavior and appearance. The community has more than 1 million members (as of October 2013) and 31,000 Developers (as of February 2014). Because of this plug-in extensibility and modular design, "The Drupal Overview" on Drupal's Web site describes it as a content management framework.