Grav - The modern open source flat-file CMS
Statamic - Build better, easier to manage websites. Enjoy radical efficiency. It's everything you never knew you always wanted in a CMS.
Bludit - Bludit is a web application to build your own website or blog in seconds, it's completely free and open source. Markdown support.
Drupal - Drupal - the leading open-source CMS for ambitious digital experiences that reach your audience across multiple channels. Because we all have different needs, Drupal allows you to create a unique space in a world of cookie-cutter solutions.
HTMLy - HTMLy is an open source databaseless blogging platform. A Flat-File Blog and Flat-File CMS written in PHP prioritizes simplicity and speed.
SilverStripe - Make Digital Transformation happen