1. Wordpress

Wordpress is a powerful yet easy to use content management system. Initially it was designed as a blogging platform. However, it slowly become popular and can be customized into a powerful CMS with some tricks and plugins. I had wrote an article about Wordpress SEO plugins and also talked about things that you should know about Wordpress 2.8.

2. Drupal

Drupal is a free and open source modular framework and Content Management System (CMS) written in PHP. It is used as a back-end system for many different types of websites, ranging from small personal blogs to large corporate and political sites.

3. Joomla

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.

4. Frog CMS

Frog CMS simplifies content management by offering an elegant user interface, flexible templating per page, simple user management and permissions, as well as the tools necessary for file management.

5. SilverStripe

SilverStripe is a PHP CMS built with Sapphire framework, and it uses MVC design pattern. you can view example sites that built with SilverStripe from the official webpage.

6. Mambo

Mambo is a full-featured, award-winning content management system that can be used for everything from simple websites to complex corporate applications. Although some Mambo sites had already migrated to Joomla, but i think i should include Mambo as it is still a great CMS.

7. TYPOlight

TYPOlight is a PHP 5 CMS and it has a lot of features such as live update, cross-browser CSS framework generator(IE7 compatible), templated based front end output, use Ajax and Web 2.0 technologies. You should check out the main page for more info.

8. Concrete5

Concrete5 is an open source content management system with simple administaror interface. You can edit a web page live by using the editing toolbar provided after you log in as administrator.

9. Textpattern

Textpattern is yet another very popular content management system. It requires PHP 4 to run and has a lot of plugins that you can use for various customizations.

10. Symphony

Symphony is a CMS that uses XML/XSLT as its templating language. Symphony lets you customize anything you like, from the website’s URL structure to your publishing environment. For a non programmer, this CMS might be complicated to learn.

11. MODx

MODx is both a PHP application framework and content management system. MODx is the first free PHP CMS to offer an API that fully supports Web 2.0 Ajax technology. It is SEO friendly CMS, and allows you to configure the meta content for each page.

12. Habari Project

Habari is a highly recommended open source blogging platform. It is being written specifically for modern web hosting environment, and uses modern object oriented programming techniques.

13. CMS Made Simple

CMS Made Simple is highly customizable and there are a lot of Modules for you to download. The Documentation is pretty complete and easy to follow.

14. ImpressCMS

ImpressCMS is a community developed Content Management System. It is highly scalable and is extremely useful for managing online communities.

15. Exponent CMS

Exponent uses an intuitive and flexible content editing system that allows website pages to be edited on the page as it is displayed. You can download modules and themes from the official website too!

16. MiaCMS

MiaCMS is a fork of the Mambo CMS. It has a powerful and extensible third party entension system, and also a flexible site theming capabilities. MiaCMS supports OpenID and can consider to be a stable and mature CMS.

17. Jojo CMS

Jojo is a search engine friendly CMS. You will have SEO friendly URL to your article, and Jojo will handle www/non-www domains for you. Beside SEO friendly, Jojo also lets you extend the functionality by adding product databases, blogs, image galleries or whatever takes your fancy.

18. TYPO3

TYPO3 is a free Open Source content management system for enterprise purposes on the web and in intranets. It offers full flexibility and extendability while featuring an accomplished set of ready-made interfaces, functions and modules.

19. Elxis CMS

Elxis CMS comes with a lot of features such as Search Engine Friendly URL, strong security, adjustable member list and complete user profiles. Its automated tasks, modern design, AJAX technology and multi-lingual interface helps you be more productive.

20. Chyrp

Chyrp is a lightweight blogging platform and it uses Twig as the templating engine. The documentation is quite complete and you can download a lot of useful modules from the main site.