I think door games have a lot of interesting similarities to modern mobile games. First, door games tended to limit you to X number of moves per day in order you to play a small bit each day. Multiplayer was sometimes much more interesting in door games (ala TradeWars) than some modern AAA mobile games that limit interactions quite a bit (such as Boom Beach). I'm surprised there hasn't been more of a renaissance of door games onto mobile devices already.