Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
Bludit - Bludit is a web application to build your own website or blog in seconds, it's completely free and open source. Markdown support.
ClassicPress - The WordPress fork. No Gutenberg. Great future!
Monstra CMS - Fast and small flat-file content management system written in PHP!
TYPO3 - TYPO3.com - Infos, SLAs, Extended Support Versions and more
Grav - The modern open source flat-file CMS