e107
e107 is a content management system written in php and using the popular open source mySQL database system for content storage. It's completely free and totally customisable, and in constant development.
Homepage: http://www.e107.org/
Support Forum: http://e107.org/e107_plugins/forum/forum.php
Joomla
Joomla! is one of the most powerful Open Source Content Management Systems on the planet. It is used all over the world for everything from simple websites to complex corporate applications. Joomla! is easy to install, simple to manage, and reliable.
Homepage: http://www.joomla.org/
Support Forum: http://forum.joomla.org/
Mambo CMS
Mambo is a full-featured content management system that can be used for everything from simple websites to complex corporate applications.
Homepage: http://mamboserver.com
Support Forum: http://forum.mamboserver.com/
PHP Nuke
PHP Nuke - open source professional portal system
Homepage: http://www.phpnuke.org/
Documentation: http://www.phpnuke.org/modules.php?name=PHP-Nuke_HOWTO
PhpWiki
A WikiWikiWeb is a web site where anyone can edit the pages through an HTML form. Linking is done automatically on the server side; all pages are stored in a database.
Homepage: http://phpwiki.sourceforge.net/
Documentation: http://phpwiki.sourceforge.net/phpwiki/
vtiger
vtiger CRM is an Open Source CRM software mainly for small and medium businesses. vtiger CRM is built over proven, fast, and reliable LAMP/WAMP (Linux/Windows, Apache, MySQL, and PHP) technologies and other open source projects.
Homepage: http://www.vtiger.com/
Documentation: http://www.vtiger.com/wiki/index.php/Main_Page
xoops
XOOPS is an extensible, OO (Object Oriented), easy to use dynamic web content management system written in PHP. XOOPS is the ideal tool for developing small to large dynamic community websites, intra company portals, corporate portals, weblogs and much more.
Homepage: http://www.xoops.org
Documentation: http://docs.xoops.org/modules/wfsection/article.php?articleid=4