GNU GPL or simply GPL is a widely used free software license. It lists terms and conditions for copying, modifying and distributing free software, created by Richard Stallman in order to protect GNU software from being made proprietary. It is a specific implementation of his "copyleft" concept.

Joomla is a free open source content management system which enables you to build Web sites and powerful online applications. Joomla is licensed under the GPL. It is written in the PHP programming language and uses the MySql data.

Mambo is a Content Management System (CMS) released under the GNU GPL for creating and managing websites through a simple web interface. It has attracted many users due to its ease of use.

Drupal is an open source modular framework and Content Management System (CMS) written in the programming language PHP. It is used as a "back end" system for many different types of Web sites. Drupal was also designed to allow new features and custom behavior to be added by third parties.