Drupal

From the Drupal website...

Come for the software, stay for the community.

Drupal is an open source content management platform powering millions of websites and applications, available cost free. It’s built, used, and supported by an active and diverse community of people around the world.

Drupal software and community offer rare value. A basic Drupal installation includes common website functions. It is fast and easy for simple sites. As a Web Development Framework, it is a superior tool for extending the basic structure to create the most complex, feature rich web applications imaginable. It is also valuable for integrating web, mobile, cloud and social media capabilities.

Drupal is an amazing success, built by a diverse, international community of highly skilled and creative people working together.