Joomla is an open source content management system (CMS) that is easy to install, user-friendly, and has an active community. It started as Mambo but was forked in 2005 to become Joomla. Key features include being built on PHP and MySQL, able to run on Linux/Unix, Windows and Mac servers, and having one-click installation through many web hosts. Resources for using Joomla include its main website, active user forums for help, and documentation wiki.