Free and Open Source Software
Joomla
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.
MODX
MODX is a free, open source content management system and digital experience platform. The CMS gives you full control over your creative, editorial vision and the experience you deliver. MODX is written in the programming language PHP and supports both MySQL and Microsoft SQL Server databases. The CMS is openly developed and released under the GPL license, and allows contribution.
TinaCMS
Tina is an open-source site editing toolkit and headless CMS for React-based sites like Gatsby & Next.js
Storyblok
A headless & API-based CMS with an opt-in head and a visual editor. With Storyblok you can manage your content through an intuitive dashboard and access that data though the content delivery API, as nested JSON. Storyblok is an open-source software and can be used as such, but is also provided as a commercially hosted, cloud rendering service. As a front-end developer you can choose to work with any template engine, framework or system of your choice.
FeinCMS
FeinCMS is a bare bones content management system written in Python on-top of the web framework Django. The CMS is built to know nothing about your content, and includes an admin interfaces that can handle content types. It lets you reorder page content blocks using a drag-drop interface, and you can add as many content blocks to a region (sidebar, header, etc) as you want. FeinCMS was built this way to allow for maximum flexibility, where developers, designers and content managers can create a unique site, tailored for their type of content and future patterns.
FrontAid CMS
FrontAid CMS is a decoupled and Git-based content management system. Content is stored in your own Git repository in the JSON text format. It works with all your current tools and you always own your data.
October CMS
October is a free, open-source and self-hosted content management system written in PHP on top of the framework Laravel. The CMS features a universal extendable dashboard, inspector, reusable CMS components and a plugin system that can be used to extend functinality of your website. The plugin store contains thousands of community-made plugins that can either be purchased or installed for free. As a data store, October CMS supports MySQL, PostgreSQL and SQLite.
Anchor CMS
Anchor is a super-simple, lightweight blog system written in PHP. Compressed, Anchor CMS weighs in at just under 250kb making it an extremely light weight content management system. With Anchor CMS, you can manage content in HTML or Markdown, depending on which you prefer. The content management is fully free and open-source and released under the GPL-3.0 License.
CushyCMS
CushyCMS is a FREE hosted content management system that's actually easy to use, fast to setup and doesn't require programming skills.