"It's not game-y," Jeff Petriello, 33, a computer Animal Crossing Bells game maker who additionally educates at the Tisch Center for the Arts, said. "On a basic level it's less about rivalry than about uniting individuals in sharing, and design is an enormous piece of that."  Quite recently, a companion halted by Mr. Petriello's island wearing the white legacy sweats of a 1990s rapper. At...