There are many CMS system to choose from and some of the most popular CMS are open source or free. All but one of the top rated CMS systems I have included are from winners of the CMSWire contest and the top hits from opensource.com.
Joomla is a free, multifunctional content management system or cms. Due to it's ease of use, it has an ever growing community of more than 40,000 users and developers. It's simple, browser-based interface makes it easy to add content pages to your website. For many people, Joomla's attraction is it's ability to be modified with the many hundreds of component addons and plugin that can be added to the website system framework. This way your website can be made to fit your needs. Also, Joomla does a good job of managing the web content needed to run the website.
Drupal is an open source CMS that is written in PHP and requires a MySQL database. It is an excellent, lightweight, flexible system which can be used to making a variety of sites from blogs to large community websites. Drupal's simple design is easy to customize and it has built-in search tool and search-engine friendly URL's as an extra add on module.
Drupal has many features for building community sites. So, it would be a good choice for a blogging or news site, but it can also support a standard website.
Plone is a free easy to install, full featured, flexible enterprise-ready CMS. However, if you want to add an extension you need a good grasp of Python and web programming. Even if you just use the default installation, you will have a very full featured website to use. Plone is built on top of Zope and has much of the extensibility that Zope has to offer. Plone would be a good fit for someone who is familiar with programming and needs a flexible, scalable CMS.
4. CMS Made Simple
CMS Made Simple has many enthusiastic reviews. It is as the name states. It is a free, very simple CMS that someone with no web experience can use to create and manage a page based website. It is very easy to add content and addons to the site. A list of modules is included in the admin interface from which the modules can be downloaded.
Unlike, Drupal, it does not have community based features such as commenting or forums. It is good for someone who just wants to add or update pages to a brochure ware website.
Mambo, formerly named Mambo Open Source or MOS, is a free, easy to use CMS. Mambo has attracted many users through it's ease in adding and managing web pages. It's more advanced features such as page caching, advanced templating techniques and robust API has attracted users who are looking for a more complex website. Mambo also offers RSS feeds, forums, polls, blogs, news flashes and etc.
Mambo is useful for creating simpler as well more complex websites.
Last, I have included WordPress among the CMS system. Both Wikipedia and Gobala Krishnan in WebPro News believe that Wordpress has expanded beyond being an open source blogging tool to becoming a CMS. Since it is enormously popular, I have added it to the list. Gobala Krishnan explains that,"it's all a matter of having clear goals and the right plugins and partnering with the right services."
For example, WordPress was used by medical blogger Graham, at Standford University's medical school, to create a Community Health Resource Center website.