b2evolution is probably the most comprehensive blog engine you can find! It includes almost any feature you could expect from a blog tool, and more! Check out the features, not to mention third party plug-ins! It runs virtually anywhere (PHP/mySQL) and it's available in many languages! 

You've just completed a gorgeous new design, ready to be released into the wild. Suddenly it strikes you, how will my client, or myself manage this content? Will I have to dive into this code to add an apostrophe, or copy-paste an ambiguous chunk of code to add a new paragraph to my front page, or post a new article?

PHP-Fusion is a light-weight open-source content management system (CMS) written in PHP4. It uses a mySQL database to store your site content and includes a simple yet comprehensive adminstration system.

PHP-Nuke is a news automated system specially designed to be used in Intranets and Internet. The Administrator has total control of his web site, registered users, and he will have in the hand a powerful assembly of tools to maintain an active and 100% interactive web site using databases.

Runcms Includes most things a webmaster would expect from a cms: downloads, links, tutorials section, polls, forums, news, faq, contact form, rss feeds, file uploads, blogging via xml-rpc, & more. Possibility to manage users as groups with module/block specific access permissions, and extend functioality.

ToendaCMS is an Open Source XML web content management system released under the GNU General Public License. You can use it for free. ToendaCMS is optimized for fast and easy setup and works on any standard webserver platform.

Your quest for a full-featured CMS/Groupware has ended! Tiki CMS/Groupware offers a very large number of features "out-of-the-box", arguably more than any other Open Source Web Application.

Ovidentia is a portal Generator for companies, organizations or communities allowing an administrable management for publications of informations, forums of discussions, shareable diaries, FAQs, Workflow, file sharing and mail interface.