Joomla!

Joomla, also styled Joomla! and sometimes abbreviated as J!, is a free and open-source content management system (CMS) for publishing web content on websites. Web content applications include discussion forums, photo galleries, e-Commerce and user communities, and numerous other web-based applications. Joomla is developed by a community of volunteers supported with the legal, organisational and financial resources of Open Source Matters, Inc.

Excerpt from Wikipedia: Joomla. Content available under CC-BY-SA 4.0.