Awesome

Live (GitHub-Flavored) Markdown Editor

Use it here

Commands

• Ctrl+L to login
• Ctrl+S / Cmd+S to save a file
• Ctrl+O / Cmd+O to open a file
• Add to query string uri=foo to share

Advanced

• Ctrl+Shift+L to login
• Ctrl+Shift+S to save locally
• Drag and drop a file into here to load it
• File contents are saved in the URL so you can share files

Feel free to take the code and copy it and modify it and use it however you like. (If you really want a licence, see WTFPL)