A free (libre), open-source (GNU GPL), content management platform designed for group collaboration. Open Atrium is based on Drupal (running on Apache, with a MySQL database).
A free (libre), open-source (GNU GPL) content management framework written in PHP with support for a number of operating-systems, web-servers and databases.
Drupal made international news following the U.S. White House's October 2009 web redesign. The variety of Drupal-powered websites demonstrates the platform's flexibility. Notable examples include British Medical Journal (BMJ); Stanford Law School, and Turner Broadcasting.
CiviCRM is an open source and freely downloadable constituent relationship management solution. CiviCRM is web-based, open source, internationalized, and designed specifically to meet the needs of advocacy, non-profit and non-governmental groups.