[stonerri]

LateX Lab was/is exactly that: http://code.google.com/p/latex-lab/

A demo is up and running at http://docs.latexlab.org/

* not affiliated with the project in anyway, just remember using it awhile back.

[beck5]

Latex lab development seemed to have stopped over a year ago before they implemented real time collaberation, if it had continued I would have not have started sharelatex.