Bludit - Bludit is a web application to build your own website or blog in seconds, it's completely free and open source. Markdown support.
Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
Grav - The modern open source flat-file CMS
TYPO3 - TYPO3.com - Infos, SLAs, Extended Support Versions and more
WonderCMS - WonderCMS is the smallest flat file CMS. Completely free, open source, privacy oriented for over 12 years.
ClassicPress - The WordPress fork. No Gutenberg. Great future!