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.

Mambo is a full-featured content management system that can be used for everything from simple websites to complex corporate applications. Features: a large and healthy user and developer community, content approval for registered users, online help, an advanced admin system, powerful templates, and more.

PHP-Nuke is a Web Portal System, storytelling software, news system, online community or whatever you want to call it. Main features include: web based admin, surveys, top page, access stats page with counter, user customizable box, themes, friendly administration GUI, option to edit or delete stories, option to delete comments, moderation system, search, etc.

Drupal is software that allows an individual or a community of users to easily publish, manage and organize a great variety of content on a website. Drupal includes features to enable content management systems, blogs, collaborative authoring environments, forums, newsletters, picture galleries, file uploads and download and much more.

PHP-Fusion is a constantly evolving content management system (CMS) powered by PHP 4 and mySQL. It provides an easy to install system with a simple yet powerful set of administrative controls. This means you will have an easy to maintain interactive community website without requiring any knowledge.

phpWebSite provides a complete web site content management system. Web-based administration allows for easy maintenance of interactive, community-driven web sites. phpWebSite's growing number of modules allow for easy site customization without the need for unwanted or unused features.

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WordPress is a state-of-the-art semantic personal publishing platform with a focus on aesthetics, web standards, and usability. WordPress features: Instant publishing, comment spam protection, themes, content management, easy upgrades, post-by-email, and more.

b2evolution is probably the most comprehensive blog engine you can find! All the features you can expect are there, including: Advanced browsing (paged, calendar, categories, search...), extended & multipaged posts, image/file upload, multiple and sub-categories, draft and quick publishing, spell checker, RSS feeds etc.