Werewolf is a game that takes place in a small village which is haunted by werewolves. Each player is secretly assigned a role – Werewolf, Villager, or Seer (a special Villager). There is also a Moderator player who controls the flow of the game. The game alternates between night and day phases. At night, the Werewolves secretly choose a Villager to kill. Also, the Seer (if still alive) asks whether another player is a Werewolf or not. During the day, the Villager who was killed is revealed and is out of the game. The remaining Villagers then vote on the player they suspect is a Werewolf. That player reveals his/her role and is out of the game. Werewolves win when there are an equal number of Villagers and Werewolves. Villagers win when they have killed all Werewolves. Werewolf is a social game that requires no equipment to play, and can accomodate almost any large group of players.
More information about the game and some tactics can be found on wikipedia page Mafia
Because the game requires between 8 – 25 people, I've set a limit of 30 people and decided to try and use upcoming.org for a signup tool. So please sign up there. I'll stick the event on geekdinner later in the month.