Found this also:

"The GeoCoin project is a combination of Cryptocurrency with GIS & GeoTechnologies. We've developed a GeoCashing interface which allows users to drop coins anywhere they like. Other community members can then go and pick up the dropped GEO right from the map using their smartphone GPS. The applications of where the coins placed are up to the user who drops them, but they can be used for scavenger hunts, promotions for businesses, outdoor recreation and more."