WordPress is a blog publishing system written in PHP. All data is stored in a MySQL database. WordPress is the official successor of b2\cafelog, developed by Michel Valdrighi. The name WordPress was suggested by Christine Selleck, a friend of lead developer Matt Mullenweg.
The latest release of WordPress is version 2.6.2, released on 08 September 2008. It is distributed under the GNU General Public License version 2.

dotCMS is a free software / open source web content management system (wCMS) for building/managing websites, content and content driven web applications. dotCMS includes enterprise CMS features such as support for virtual hosting, WebDav (beta) ,structured content, clustering and can run on multiple databases PostgreSQL, MySQL, MSSQL and Oracle, and is available as software that can be installed on a web server or via a hosting provider (dotMarketing is now offering the onDemand virtual hosting service for clients, and has also registered an image available via the Amazon Elastic …

Plone is a free and open source content management system built on top of the Zope application server. It is suited for an internal website or may be used as a server on the Internet, playing such roles as a document publishing system and groupware collaboration tool.
Plone is released under the GNU General Public License (GPL) and is designed to be extensible. Major development is conducted periodically during special meetings called Plone Sprints. Additional functionality is added to Plone with Products, which may be distributed through the Plone website …

PacktPub.com has been accepting MVP nominations since early July and for the majority of Content Management Systems

Joomla is an award-winning content management system (CMS), which enables you to build Web sites and powerful online applications. Many aspects, including its ease-of-use and extensibility, have made Joomla the most popular Web site software available. Best of all, Joomla is an open source solution that is freely available to everyone.