Joomla!
From Joomla! Documentation
Joomla! is a powerful Content Management System (CMS) used to power all kinds of websites all around the world. The benefits of Joomla! include:
- Easy Installation
- Simple website maintenance
- Top-notch security and stability
- Powerful free and commercial extensions
- Plentiful templates to easily change the look of your website
Main Joomla! website: www.joomla.org
Joomla Support forums: forum.joomla.org