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.
Pokemon Go has been the most successful at implementing this concept so far. Its success will likely spawn other apps that build on the idea.
Do you know of any other games that use the real world as the game map? Let me know in the comments.