Drupal is a free software package that allows an individual or a community of users to easily publish, manage and organize a wide variety of content on a website.
Geeklog is a PHP/MySQL based application for managing dynamic Web content. “Out of the box”, it is a blog engine, or a CMS with support for comments, trackbacks, multiple syndication formats, spam protection, and all the other vital features of such a system. The core Geeklog distribution can easily be extended by the many community developed plugins to radically alter its functionality. Available plugins include forums, image galleries, and many more.
LifeType is an open-source blogging platform with support for multiple blogs and users in a single installation.
Nucleus CMS offers the ability to set up one or more blogs. You can even show the contents of multiple weblogs on the same page. Each blog can have one or authors and an author can be permitted to post or even to change settings for the blog itself.
PivotX is free software to help you maintain dynamic sites such as weblogs, online journals and other frequently updated websites. It’s written in PHP and uses MySQL or flat files as its database.
Serendipity is a PHP-powered weblog application which gives the user an easy way to maintain an online diary, weblog or even a complete homepage. While the default package is designed for the casual blogger, Serendipity offers a flexible, expandable and easy-to-use framework with the power for professional applications.
WordPress is a state-of-the-art publishing platform with a focus on aesthetics, Web standards, and usability. WordPress is both free and priceless at the same time.
WordPress allow for multiple sites under a single install. This process is call “Multi-site” and is built into all WordPress Installations. You just need to enable multi-site through changes to a few files.