Mockingbird : Mockingbird is an online tool that makes it easy for you to create, link together, preview, and share mockups of your website or application.
HedgeDoc : HedgeDoc (formerly known as CodiMD) is an open-source, web-based, self-hosted, collaborative markdown editor.
You can use it to easily collaborate on ...
Etherpad is an Open Source online editor providing collaborative editing in really real-time powered by Node.js
