If another driver around you is breaking a law dial 911 if it's an emergency (drunken driving) or the non emergency number if it's small (littering). In the first case you should let the police deal with it and in the second you need to be able to positively identify the driver and be willing to show up in court. You can do this today and don't need to have an iphone app that bypasses legal channels and the the other drivers right to due process.