Joomla! is an open source content management system (CMS) to build websites and web applications. With powerful features, ease of use and extensibility, Joomla has become one of the most popular website software. With Joomla! you get access to thousands of free extensions and templates allowing to build a site to fit your specific reguirements.
If you develop websites for your customers, Joomla! is a great tool for you. Designed to be easy to install and set up, even for unexperienced users, and with a short learning curve.