oh! found a cross platform app... checking it out now
EDIT: its called Scavify... not nearly as good as the apple apps i found, but it is a lot more polished i guess... BUT over 5 people/event and its $500!!! wtf... i guess us organizers could all create the same event and have it password protected so each event has 5 teams assigned to it... it also doesnt seem to let you combine a checkin with a question to unlock the next location... the hunt continues but i think we can use an app for sure