VSAnywhere is good for that on live projects.

https://vsanywhere.com

(no affiliation)

If you're into the js/html/css party, Plunker is a more IDE-like experience that has real-time collaboration built-in.

http://plnkr.co/edit/?p=preview&s=RxFWQJqa5yVe8qI5

you should then try http://liveweave.com. they have code-hinting for HTML5, CSS3, JS, jQuery...really awesome stuff. I recently found it, and loving it so far.

JSFiddle has had this for a while.

But for .NET, that's what makes it neater. JSFiddle collab has been helpful, now we have it in .NET too :D

Good for GUI, but for business logic we need the real deal :).