Joomla! is a free open source content management system for publishing content on the World Wide Web and intranets. The system includes features such as page caching to improve performance, RSS feeds, printable versions of pages, news flashes, blogs, polls, website searching, and language internationalization. Joomla is licensed under the GPL, and is the result of a fork of Mambo.
The name Joomla officially ends with an exclamation mark, but this is commonly omitted.
It is written in the PHP programming language and uses the MySQL database by default.
Joomla came into being as the result of a fork of Mambo by the development team on August 17, 2005. At that time, the Mambo name was trademarked by Miro International Pvt Ltd, who formed a non-profit foundation with the stated purpose to fund the project and protect it from lawsuits. The development team claimed that many of the provisions of the foundation structure went against previous agreements made by the elected Mambo Steering Committee, lacked the necessary consultation with key stake holders and included provisions that violated core open source values.
Read more about Joomla at Wikipedia.
I am using Joomla! since 2004. Besides installing and configuring it, I have experience in modifying code of Joomla! and it's extensions to achieve different behavior than default one. Most of my Joomla! project required such changing of Joomla! and it's extensions.