Etherpad did this for one of Paul Graham's essays, but sadly they were bought out and it's no longer there. Apparently it was at http://etherpad.com/ep/pad/slid

Etherpad did this for one of Paul Graham's essays, but sadly they were bought out and it's no longer there. Apparently it was at http://etherpad.com/ep/pad/slider/13sentences http://etherpad.com/ep/pad/slider/13sentences