ClassicPress - The WordPress fork. No Gutenberg. Great future!
Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
TYPO3 - TYPO3.com - Infos, SLAs, Extended Support Versions and more
Concrete CMS - Concrete CMS is an open source content management system for teams. A website builder with built in tools make editing content easy.
Textpattern - Textpattern is an elegant content management system that is free, open source software.
Anchor CMS - Free and lightweight blogging system