If you like first person shooters, paint ball, or just to interact with your friends who are, then check out this awesome game idea.
Father.io is a free open world AR shooter game that uses your smartphone as your gun.
It is based on Augmented reality (AR) and developed by Proxy42, a company established in 2012 by gamers, for gamers. Father.io is geared to be a Real Life Massive Multiplayer First Person Shooter that interacts with the gamer, their environment and other gamers.
Father.io uses Ingress (a different AR game) as a base concept. Ingress has two opposing forces battling over real-world territory. Father.io takes it a step further by enhancing the game experience through the use of a 363R Trigger, which can be connected to your smartphone and used to shoot players that are within 50 meters of you.
This is currently a worldwide gaming project and sounds like a ton of fun. Check out their videos on Youtube and their website.