Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
VuePress - A static site generator by Vue.js 🛠️
ClassicPress - The WordPress fork. No Gutenberg. Great future!
Forestry.io - A simple CMS for Jekyll and Hugo sites.
Textpattern - Textpattern is an elegant content management system that is free, open source software.
Publii - Open Source CMS for Static Websites