This is pretty much self-moderating as well as simple. Any number can play in a round, though at least 12 people would be nice.
As of February 5, 2011, when a new round starts, you have 48 hours to board the Ferris wheel. Each player in a round does so at random. At the top of the wheel is a gun that can be used to obliterate any player's seat. Once it gets to be your turn, select one player you would like to kill. That player immediately loses the game. However, you only have 48 hours to make your decision. Unless it's the first turn of the round, time is measured from the last death, not from the mod update. If you run out of time, you die. Effective June 28, 2012, the mod will make a reasonable attempt to give you a 24-hour warning before you time out, but be aware that his or her schedule may not match that of the previous killer's and the time of the last death remains the official starting point. For example. if the warning is two hours late, you have 22 hours from the warning to kill and not 24.
When it's not your turn, however (and if you are still alive), you are allowed to plead with the shooter, make alliances with other players, or otherwise convince the shooter to kill somebody other than you.
The last person alive on the wheel wins and gets to take signups for the next round. The game moderator has the option of whether or not to board the wheel, but cannot moderate two consecutive rounds. If the moderator boards the wheel and wins, the runner-up mods the following round.
Minor change to the rules since I didn't think of it when I wrote them:
The last person alive on the wheel wins and gets to take signups for the next round. The game moderator has the option of whether or not to board the wheel, but cannot moderate two consecutive rounds. If the moderator boards the wheel and wins, the runner-up mods the following round.