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.
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.
Cleartext - A text editor that allows only the 1,000 most common words
Visual Studio Code - Build and debug modern web and cloud applications, by Microsoft
Quill - Powerful, API-driven rich text editor
Vim - Highly configurable text editor built to enable efficient text editing