Joomla!

Joomla is a free and open-source content management system (CMS) for publishing web content. 

It is built on a model–view–controller web application framework that can be used independently of the CMS (Wikipedia).

Training

• Beginners Tutorials - Joomla! Documentation

• SiteGround - Joomla Tutorial - How-Tos for Beginners

Also See

• Drupal

• Google Sites

• WordPress