I like the simple stuff that blows you away. EtherPad is one of those things.
You go to the site, start typing stuff, and then simply send the URL of the page to someone (or multiple someones) and you’re instantly sharing that document. You each see what the other person or people are typing, and their text is highlighted so you can clearly see who typed what.
Then you can export it, etc., as you would expect. So clean. Check out this screencast to get a better grasp of it. ::