SilverStripe

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CppCMS

Joomla is a free and open-source content management system written in PHP. The CMS is built entirely by volunteers from all over the world and has a strong community that provide educational resources, and extensions. 

Django CMS is a free and open-source content management system build on the Python web framework Django. With Django CMS, you can create your own website or blog in a matter of minutes which is easy to maintain far into the future. If you are a developer utilizing the Django framework you can integrate Django CMS into an exiting Django application and take advantage of it's publishing and editing features.

CMS Made Simple is a free and open-source content management system that offers an easy to use interface for end users, while maintaining a powerful backend for developers. CMS Made Simple is written in PHP and got an extensive API and custom modules. The CMS also utilize the Smarty templating engine that can be used to customize sites with HTML, CSS and PHP.

Backdrop is a full-featured content management system written in PHP. The Backdrop CMS allows non-technical users to manage a wide variety of content. It can be used to create all kinds of websites including blogs, image galleries, social networks, intranets, and more.

With Contentstack, content and marketing teams are able to publish content with a much higher frequency than ever before. Contentstack brings business and technology teams closer together by providing a personalized, omnichannel experience with a visual editor alongside content scheduling and publishing management tools.

Grav is a modern free and open source flat-file content management system. With Grav, you can publish content and build sites in a fast, flexible and simple manner with the file-based web platform. Grav requires zero installation and is just an zip archive that can be extracted to start using the CMS. Grave also comes with a powerful package management system that allow you to extend the feature set of Grav CMS. With the package management system you can install and upgrade themes and plugins written specifically for Grav. The software is written in PHP and released fully free and open-source under the MIT License.