Free Software
WonderCMS
WonderCMS is the smallest flat file content management system. The CMS is built with PHP and has been developed since 2008. No initial configuration required to setup the WonderCMS, the installation is straight forward and simply requires you to unzip and upload 5 files.All data within WonderCMS is structured as JSON format and the flat file nature of the content management system also allow you to migrate hosts easily by transfering files across, no database migration required.
Exponent CMS
Exponent CMS is a notable free and open source content management system that contains its own independent modular software framework of enterprise level.
Daptin
With Daptin you can build faster, more capable APIs over your data that works across all types of frontend. Daptin is a free and open-source headless CMS server written in Go. Daptin can be used as a backend for both mobile and web applications and provide ready-to-go REST and GraphQL API infranstructure.
Mura
The Mura CMS platform makes it easier & faster to build and update websites. The content management system was created to free content managers from distraction of multiple tools, the worry of steep learning curves, and a clear need to tell the right story, to the right audience, at the right time. Mura is loved by content managers, content contributors, marketers and developers alike.
Bludit
Bludit is a content management system that allow you to build your own website or blog in seconds, it's completely free and open source. Markdown support. The flat file architecture of Bludit makes your websites extremely fast, while still allow you and your team to manage content the way you would in other popular content management systems like WordPress, Joomla and Drupal. Without relying on databases like MySQL or complicated DevOps workflows.
Quanta CMS
Quanta is a free, open source Content Management Framework thought for programmers and used for the creation of new-generation websites and applications.
Cockpit
Cockpit is a self-hosted headless and api-driven CMS. With Cockpit you can manage any structured content for your website, web app or mobile application. Cockpit's intuitive dashboard allow anyone to manage content without technical skills and is a perfect match for developers and teams looking to improve they content management situation. Cockpit allow you and your team to setup a content management system for static sites and JavaScript-based front-ends in no-time.
OpenCMS
OpenCMS is based on Java and XML technology that allows you to build highly customizable and interactive websites and portals. The open-source content management system includes a WYSIWYG editor and fully-featured Template Engine which is fully compliant with W3C standards.
Django CMS
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.