I was doing some browsing, well Stumbling to be exact, and came upon a great new site called Scratchpad. Developed by Nathan Bashaw, Scratchpad serves as a great place to experiment and play around with your HTML, CSS and even Javascript. You get a dual-pane view; you’re code on one side, and a live render of your code on the other pane.
Every single document gets it’s own URL, and gets saved automatically every single time you make an update. To boot more than one person can work on the same exact file, at the same exact time. As soon as you make any change – it’s instantly mirrored on the other persons display.
Head on over to http://scratchpad.io to check it out. I have also listed Scratchpad in our Free Webmaster Resources Directory, just in-case you ever forget the link.