Drupal is a mature, robust and powerful open-source Content Management System (CMS) that allows you to easily manage all your web content without the need for any technical knowledge of web coding.
Drupal’s core modules are maintained by a small, select panel of developers, including the original author and chief controller of the software. This panel is supported by a development community of over 31,000 members, with over 16,000 modules available in the Drupal product set.
Social Change Media's own experience with Drupal can be summed up by the fact that we've produced dozens of websites using Drupal and never had a client requirement that we haven't been able to meet with the Drupal product set.
For more information about Drupal see: drupal.org