Basic useful feature list:

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

I'm no good at writing sample / filler text, so go write something yourself.

Look, a list!

• foo
• bar
• baz

And here's some code!

$(function(){
  $('div').html('I am a div.');
});

This is on GitHub so let me know if I've b0rked it somewhere.

Props to Mr. Doob and his code editor, from which the inspiration to this, and some handy implementation hints, came.

Stuff used to make this:

• marked for Markdown parsing
• CodeMirror for the awesome syntax-highlighted editor
• highlight.js for syntax highlighting in output code blocks
• js-deflate for gzipping of data to make it fit in URLs