Drupal (pron.: /ˈdruːpəl/) is a free and open-source content management framework (CMF) written in PHP and distributed under the GNU General Public License. It is used as a back-end system for at least 2.1% of all websites 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.
The standard release of Drupal, known as Drupal core, contains basic features common to content management systems. These include user account registration and maintenance, menu management, RSS feeds, page layout customization, and system administration. The Drupal core installation can be used as a brochureware website, a single- or multi-user blog, an Internet forum, or a community website providing for user-generated content.
Also See Network Empire Project
Also See One Web Ring to Rule them All
Also See The PLMM (Perpetual Lead Magnet Machine) Intereactive Tutorial