The mother of all demos
sloan.stanford.edu
sloan.stanford.edu
"We are as gods and might as well get good at it" - Whole Earth Catalog (1969)
"We are as gods and have to get good at it." - Whole Earth Discipline (2009)
In some sense, it's still better than current shared-editing systems, an early and more structured Google Wave, if you will.
Very impressive.
That said, the demo by Doug Engelbart from 1968 (which is what you should have used as a title) is very impressive. I saw it ten years ago in my human-computer interaction course, and everyone was completely blown away by it then, and it's still very impressive.