Mafia is a horrendously political game with deceptively simple rules. The players are divided into two teams, the Honest Citizens and the Mafia. Each team is trying to kill all the members of the other team. The problem is that not everyone knows who is who. The Mafia recognise each other, but the Honest Citizens do not know who is Honest and who is a Mafioso. The Honest Citizens may outnumber the Mafiosi and so could hold the upper hand, if only they could trust each other.
Each night the Mafia choose a victim to murder. That player is out of the game.
Each day, the whole population get together and vote on who to lynch. If a majority of players agree, then the selected player is out of the game. Only after they die do the Honest Citizens discover whether they killed an enemy, or a friend.
Days and nights alternate until only one team is left. They are the winners.
The Honest Citizens have one trump card: the "Angel". The Angel is one of the Honest Citizens. Her identity is a secret and generally she is wise to keep it that way. Each night, after the Mafia have done their dirty work, the Angel is able to investigate a single player and discover whether or not they are Mafia. She can use this information however she likes, but must be careful not to make too much of it, or else she may well be the next one on the Mafia's hit list.
Full details of how the game is played, along with descriptions of strategy and dozens of variations can be found at:
http://www.princeton.edu/~mafia/The game can be played online at:
This game is not nomic, in that the rules are not changeable. The only thing that is changeable is that the number of mafia members and citizens can be changed.