Idea for smartphone app whereby its a mass roleplay system where people are infected or survivors and infected get to tag survivors to turn them. Like a survivor might be in a cafe somewhere and nearby an infected and the app is such they can see other players so the infected comes to the cafe and within a certain distance tags the survivor turning him. Or else the survivor hunts infected using his smartphone as a long range weapon 'shooting' infected he locates on his screen by getting to a certain distance and scanning them. Also perhaps survivors have to salvage resources to live and there might be various ways of obtaining this like scanning barcodes from supermarkets of food items "abandoned" supermarkets and so on.
Maybe different factions of survivors.
These are just examples of how I see the ap working as in essence a crowd networking cross rpg of zombies and survivors
But Im guessing tech guys could make it even better than it sounds here.