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.
CKEditor - Real-time collaborative future-ready rich text editor
Bit.ai - Bit is a smart real-time document collaboration platform for teams to create interactive documents, manage digital content and track document insights.
Summernote - Summernote is a JavaScript library that helps users create WYSIWYG editors online.
Airborn - Create and edit documents online without sacrificing your privacy
Froala Editor - Froala Editor is a WYSIWYG HTML editor that enables rich text editing capabilities for the applications.