It might be fun to have an RPG game app for your mobile phone where the game map is the real world in real-time. You have to travel in real life to get to different places within the game. Going to a real world location lets you play at that location in the game. For example, a specific Starbucks in Miami might correlate to a bar, or dungeon, or a Starbucks in-game. If two players in the real world are playing at the same location, they will meet each other in the game.
Perhaps such an app can be monetized by correlating real-world purchases at different locations with in-game items or power-ups. That way real world businesses gain when people play the game at their shops. For example, purchasing a drink at a Starbucks in real life may give your game character a potion of some sort for use in the game.
Do you know of any games that use the real world as the game map? Let me know in the comments.