Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
DEV.to - Where software engineers connect, build their resumes, and grow.
TYPO3 - TYPO3.com - Infos, SLAs, Extended Support Versions and more
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.
ClassicPress - The WordPress fork. No Gutenberg. Great future!
Portfolio CMS - Portfolio CMS is an open-source, highly customized blog and CMS written in Redux and Rails API.