MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
Sitecake - Drag and drop CMS for HTML websites. It's flat file CMS so it's pretty fast.
TiddlyWiki - a non-linear personal web notebook
ClassicPress - The WordPress fork. No Gutenberg. Great future!
Confluence - Confluence is content collaboration software that changes how modern teams work
TYPO3 - TYPO3.com - Infos, SLAs, Extended Support Versions and more