Drupal / Joomla
Drupal and Joomla are both free and open-source content management system (CMS) and content management framework (CMF) written in PHP.
Dot Net Nuke
The DotNetNuke (DNN) content management system is intended to allow management of websites without much technical language, and extensible through third-party modules.
WordPress is a free and open source blogging tool and a dynamic content management system (CMS) based on PHP and MySQL.
SharePoint is a web application platform and has historically been associated with intranet content management and document management.