It's called Woop.ie (Write Only Once, Publish It Everywhere), and we have a small number of customers at the moment. We just have a holding page here: http://woop.ie but our demo page was live and allowed magazine creation, issue building, previewing, etc. It got some visitors from yc. Unfortunately guess it wasn't enough this time around.
We'll keep working on it obviously. Considering applying to Brooklyn Beta summer camp, actually, anyone else?