Firepad - Open source collaborative code and text editing that relies on Firebase for real-time data...
Google Docs - Create a new document and edit with others at the same time -- from your computer, phone or tablet. Get stuff done with or without an internet connection. Use Docs to edit Word files. Free from Google.
CryptPad - CryptPad is a collaborative office suite that is end-to-end encrypted and open-source.
Bit.ai - Bit is a smart real-time document collaboration platform for teams to create interactive documents, manage digital content and track document insights.
eduPad - Real-time collaborative text-editor. No account required. Edits highlighted in authors color.
Airborn - Create and edit documents online without sacrificing your privacy