WordPress is a free and open-source content management system (CMS) based on PHP and MySQL. Features include a plugin architecture and a template system.

Drupal is content management software (CMS). It’s used to make many of the websites and applications you use every day. Drupal has great standard features, like easy content authoring, reliable performance, and excellent security.

Joomla! is an award-winning content management system (CMS), which enables you to build web sites and powerful online applications.