It is Forbidden

From the Introduction:
It Is Forbidden is a team-based story game of creating cultures – two separate
cultures – while also roleplaying out the tragic consequences when the
cultures mix. The cultures are built on a framework not based on what they
produce or what they value, but what they forbid: their superstitions, bans,
heresies and taboos. The things that are forbidden keep our deepest fears at
bay, and reveal our darkest desires, and fear and desire make a society.
The game is for 4 to 20 players. It does not require a GM. It takes about two
hours to play one session, depending on how many players you have.
The essence of the game players taking turns to add to a list of laws, customs
and superstitions, things that are forbidden by their tribe. With each round,
the importance of the laws and the consequences of breaking them escalates.
At the end of the game, the two lists provide an insight into two separate
cultures, and the scenes played out will provide a sense of how those cultures
interact and conflicts that will emerge in that interaction. This information
can then be used as a basis for further creative exploration, but it is the end
point of this game.