Mambo

Mambo

Mambo is a full-featured content management system that can be used for everything from simple websites to complex corporate applications. Continue reading for a detailed feature list.Source code is completely free.
A large and healthy user and developer community.
Provides a basic level of content approval for registered users.
Online help.
Page caching mechanism to improve performance on busy sites.

Trash manager
Advertising management (banners, etc).
Media (images, documents) upload and management.
Content display scheduling.
Content syndication (RSS).
Search engine friendly (SEF) URL's.
Internationalisation (interface translation).
Content macro language (aka mambots).
Advanced and separate system administation system.
Advanced package/addon/template deployment system.
Simple but powerful template system (written mostly in HTML, no complex templating syntax to learn, just a couple of PHP functions to include).
Heirarchial user access groups.
Basic visitor statistics.
Multiple WYSIWYG content editor support.
Simple polls.
Content voting/rating system.null

Many more free addons are available at mamboforge.net. Some of these addons include:
LDAP authentication
Extended user profiles
Forums
Media galleries
Document managers
Templates
Events calendar

and many, many more...