1. WordPress
WordPress started in 2003 with a single bit of code to enhance the typography of everyday writing and with fewer users than you can count on your fingers and toes. Since then it has grown to be the largest self-hosted blogging tool in the world, used on millions of sites and seen by tens of millions of people every day. And the most its free.
2. 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.
3. Drupal
Drupal is a free software package that allows you to easily organize, manage and publish your content, with an endless variety of customization.
4. ExpressionEngine
ExpressionEngine, or “EE,” is a multi-purpose content management system developed by American software company EllisLab. It is a modular web platform that offers three tiers of licenses: Freelancer, Non-Commercial, and Commercial.
5. TextPattern
Textpattern is a free open source content management system unlike any other; it allows you to easily create, edit and publish content and make it beautiful in a professional, standards-compliant manner.
6. Contao (formerly TYPOlight)
Contao is an open source content management system (CMS) for people who want a professional internet presence that is easy to maintain. The state-of-the-art structure of the system offers a high security standard and allows you to develop search engine friendly websites that are also accessible for people with disabilities.
7. SilverStripe
SilverStripe CMS is an open source web content management system used by governments, businesses, and non-profit organisations around the world. It is a power tool for professional web development teams, and web content authors rave about how easy it is to use.
8. Umbraco
Umbraco is one of the most deployed Web Content Management Systems on the Microsoft stack. It's in the top five most popular server applications and among the ten most popular open source tools in general.
9. concrete5
Many content management systems are focused on developer or site owner needs, but concrete5 is a CMS that truly delivers the best to both worlds. An in-context editing toolbar makes it easy to make changes as you navigate the live website. A truly MVC architecture and API make it easy for developers to truly use the CMS as building blocks.
10. CushyCMS
CushyCMS is the only hosted CMS on this list. There’s a limited-feature free version that includes an unlimited number of sites, pages, and editors, but doesn’t let you use your own logo or your own domain name for the admin panel, or customize the admin experience.