Joomla!
From Joomla! Documentation
Joomla! is a powerful Content Management System (CMS) used to power simple to corporate website all over the world. The benefits and features of the Joomla content management system include:
- Easy Installation
- Easy website maintenance
- Joomla! has lots of built-in features: Mass Mailing, Banner Management, SEF (Search Engine Friendly urls), and much more...
- Thousands of FREE and commercial extensions available on http://extensions.joomla.org/
- Many free and commercial templates are available to make your website attractive
Main Joomla! website: http://www.joomla.org
Joomla Support forums: http://forum.joomla.org/