Joomla! is a powerful open source portal system, and is one of the most-used scripts on the Internet. Joomla! forked from the Mambo project in 2005.
From the Author
Joomla! is one of the most powerful Open Source Content Management Systems on the planet. It is used all over the world for everything from simple websites to complex corporate applications. Joomla! is easy to install, simple to manage, and reliable.
Authors website: http://joomla.org