Drupal is a popular open source PHP-based CMS. There is a Drupal Stack Exchange at http://drupal.stackexchange.com/, so if your question is related to Drupal but not Pro Webmasters, then it should be asked over there.
Drupal has a very active community and thousands of contributed modules (plugins) and themes. Download them at [drupal.org].
- Website: https://www.drupal.org
- Drupal API: https://api.drupal.org
- Wikipedia: http://en.wikipedia.org/wiki/Drupal
- Drupal.SE: http://drupal.stackexchange.com