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
TinyMCE - TinyMCE is a content editor that functions as a plug-in for Wordpress websites.
Quill - Powerful, API-driven rich text editor
Sublime Text - Sublime Text is a sophisticated text editor for code, html and prose - any kind of text file. You'll love the slick user interface and extraordinary features. Fully customizable with macros, and syntax highlighting for most major languages.