Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
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!
Chyrp Light - An active fork of Chyrp, an ultra-lightweight blogging engine, written in PHP.
Textpattern - Textpattern is an elegant content management system that is free, open source software.
django CMS - Enterprise Content Management with Django The open-source CMS used by thousands of websites since 2007