DokuWiki - DokuWiki is a simple to use and highly versatile Open Source wiki software that doesn't require a database.
Firepad - Open source collaborative code and text editing that relies on Firebase for real-time data...
TiddlyWiki - a non-linear personal web notebook
CryptPad - CryptPad is a collaborative office suite that is end-to-end encrypted and open-source.
MediaWiki - MediaWiki is a free software wiki package written in PHP, originally for use on Wikipedia.
eduPad - Real-time collaborative text-editor. No account required. Edits highlighted in authors color.