Is anyone here familiar with multiplayer, turn-based games that can be played non-simultaneously?

By that, I mean games where the 2+ players involved don't need to be online at the same time. An old example is play-by-mail chess: two players would mail their moves to each other, slowly progressing as each person makes a move then sends the results to the other. I'm sure there are some e-mail-based options to do the same nowadays.

I'm having trouble being online at the same moment as some people when it comes to play games. Having an option where we don't need to be online at the same time to progress would be interesting, even if games end up taking much longer as a result. Maybe some of you have played that way before, so I thought I'd see if anyone had something to share.

I was just thinking yesterday that this kind of gameplay would work for some board games such as Risk. After the initial setup, one player makes all his attacks and moves. Control is then forwarded to the next player, who might have his play session on the following day. The next person is then able to make its strategies, and so the game goes...

Anyone know of such a setup?