In De Profundis, an important part of the game is writing and sending letters to the other players. It's played in real-time with mail correspondence being the only form of contact between players. It's usually done by writing traditional snailmail for the sake of immersion.
This is the only game of that kind I've seen, but I'd like more alternatives. Any such game would do, but I suppose that free-form RPGs would better suited for this since the players can't make decisions very often. Is there any other?
I'm looking both for systems and scenarios to play with my friends.