AKA: Play By Email. (It doesn't have to be email, but that seems to be the primary method, an has been for multiple decades.)
I've been doing this for about 13 years now. Got started in Star Trek RP, and was instantly hooked.
For those who don't know what simming is, it is basically cooperative narrative RP. (The does a passable definition.) The GM offers a setting and a scenario that the players then respond to. (EG: "You're on your ship, and the warp core is about to breach.") It's different than a system-based game in that there are no dice to roll. As long as you stay true to your character, and don't railroad others' characters, your posts should be fine. An interesting side effect is that players can create their own subplots. Complications and/or additions that make the game more interesting.
Right now I play on a Star Trek game and a Stargate game. Though it looks like I may get roped into two other Trek games that some people I know have threatened to spin up.
Anyone else play this sort of thing?