Concrete CMS - Concrete CMS is an open source content management system for teams. A website builder with built in tools make editing content easy.
ClassicPress - The WordPress fork. No Gutenberg. Great future!
django CMS - Enterprise Content Management with Django The open-source CMS used by thousands of websites since 2007
Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
Kirby - Kirby is a website for businesses to use to sort contacts and other information. The site is easy to use and features several details for businesses of all sizes.
TYPO3 - TYPO3.com - Infos, SLAs, Extended Support Versions and more