Penflip - Typewrite is a real-time collaborative writing environment with Markdown support, versioning and Dropbox syncing. Alternatives to Penflip for Web, Windows, Mac, Linux, iPhone and more.
CKEditor - Real-time collaborative future-ready rich text editor
Cleartext - A text editor that allows only the 1,000 most common words
Summernote - Summernote is a JavaScript library that helps users create WYSIWYG editors online.
Quill - Powerful, API-driven rich text editor
Froala Editor - Froala Editor is a WYSIWYG HTML editor that enables rich text editing capabilities for the applications.