Slitherine

This feature exists, but is currently undocumented. To start a game in hot seat mode:
1. Go to new scenario screen.
2. Select your scenario and settings.
3. Hold shift when you press the 'Play' button.

Interestingly enough, this also works for campaigns. A subtle hint that, someday, multi-player campaigns may become a reality (Awesome!).

BTW, it was a pretty hilarious conversation:

[6:22:58 PM] Kerensky: Oh
[6:22:59 PM] Kerensky: I used a 170mm
[6:23:34 PM] Kerensky: BTW plz implement hot seat mode soon, I want to be able to play both sides for play testing purposes
[6:23:39 PM] Kerensky: soon as possible
[6:23:50 PM] Mr X: Hold shift when you hit "Play" in game setup.
[6:23:55 PM] Mr X: It will start in hot seat.
[6:24:42 PM] Kerensky: Well
[6:24:44 PM] Kerensky: I'll give you this
[6:25:11 PM] Kerensky: When it comes to implementing something "As Soon As Possible" it doesn't get any faster then that!
[6:25:20 PM] Mr X:
[6:25:29 PM] Kerensky: Well played, well played