Software
Strapi
Strapi is a free and open source headless CMS developed with JavaScript for Node.js. The software makes it really simple to generate REST and GraphQL APIs. Simply create your database schema and relationships in the Strapi admin panel UI, and Strapi will auto-generate API endpoints to represent the data structures provided. Strapi comes packed with features you come to expect from normal CMS's such as authentication, authorization, content management and a media library. The software can be used for free and can be self-hosted on any server and platform. Extra enterpise functionallity is currently being developed, and will be sold at cost.
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.
PhpSQLiteCMS
phpSQLiteCMS - a simple & lightweight CMS
Progress Sitefinity
Sitefinity's web content management software is a marketing command center to drive growth for your business. Easily manage multi-site experiences deployed your way.
Bear CMS
Bear CMS is a self-hosted content management system that seamlessly integrates with your website. With Bear CMS you own your data and content, which is store on your own server. Your websites and Bear CMS's management tools integrate seamlessly and creates an experience that content managers and editors will enjoy.
TinaCMS
Tina is an open-source site editing toolkit and headless CMS for React-based sites like Gatsby & Next.js
Ponzu CMS
Ponzu is a powerful, free and open-source HTTP server framework and CMS. It provides automatic, free, and secure HTTP/2 over TLS with Let's Encrypt, a useful CMS and scaffolding to generate content editors, and a fast HTTP API on which to build modern applications.