[Kyrio]

I used to play a lot of Daifen [1], a French play-by-mail game that blends strategy, diplomacy and role play. Games can last about a month, with different game speeds (one turn per day, three turns per week, etc.) It's still up, though the player count isn't what it used to be. You can do everything in the interface, from sending orders to planning battles to contacting other players, but the core mechanic of play-by-mail is still there. I sometimes toy with the idea of making an international version...

[1] https://www.daifen.com/index.php