Drupal

Drupal is an open source web content management framework for building Internet portals, corporate web site, e-commerce sites, and more.

Drupal is used to build web sites. It's a highly modular, open source web content management framework with an emphasis on collaboration. It is extensible, standards-compliant, and strives for clean code and a small footprint. Drupal ships with basic core functionality, and additional functionality is gained by the installation of modules. Drupal is designed to be customized, but customization is done by overriding the core or by adding modules, not by modifying the code in the core. It also successfully separates content management from content presentation.