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.
More information: http://www.joomla.org
Mambo is a full-featured content management system that can be used for everything from simple websites to complex corporate applications. Mambo has a large and healthy user and developer community. The software itself includes some great features including: advertising management (banners, etc), content display scheduling, content syndication (RSS) & search engine friendly (SEF) URL’s.
More information: http://www.mamboserver.com
Drupal is a free software package that allows an individual or a community of users to easily publish, manage and organise a wide variety of content on a website. Tens of thousands of people and organisations are using Drupal to power scores of different web sites. The built-in functionality, combined with dozens of freely available add-on modules, will enable features such as: E-Commerce, Blogs, Forums, Newsletters & Podcasts etc.
More information: http://www.drupal.org
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, although a blogging platform can also be used as a Content Management System with very few tweaks (e.g. creating a static homepage) to how WordPress is intended to function (e.g. creating a static homepage). There are 1000s of themes & plugins available for WordPress, allowing users to create bespoke websites & themes.
More information: http://www.wordpress.org