@timotheus The original Gamecube Animal Crossing did this in an incredible low-tech way: http://animalcrossing.wikia.com/wiki/Item_codes_(GCN) in-game it would say "sending thing to your friend, give them this code" but there was of course no networking, it was just a hardcoded hash. Clearly abusable, not for competitive play, but I always thought that was really clever.