Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
Lavalite - PHP CMS built with Laravel and Bootstrap.
ClassicPress - The WordPress fork. No Gutenberg. Great future!
Blogsvertise - Blogsvertise is an influencer marketing software designed to help businesses discover content creators, collaborate with influencers, and manage marketing campaigns on a centralized platform.
Textpattern - Textpattern is an elegant content management system that is free, open source software.
ApostropheCMS - Apostrophe is a powerful website builder platform built on an enterprise open source CMS, offering in-context live editing, visual design tools, and multisite enablement in a full stack JS environment.