Werewolf, designed by Dimitry Davidoff and originally released in 1986, is a public domain game. An alternative version is known as Mafia.
More About Werewolf / Mafia:
Werewolf takes place in a village infested by two or more werewolves (depending on the total number of players). Each player is secretly assigned a role, which in the baisc game could be werewolf, villager, or seer. At night, the werewolves kill a villager. During the day, the remaining villagers choose someone they suspect to be a werewolf and lynch that player.
Werewolves win when there are an equal number of villagers and werewolves; villagers win when they have killed all of the werewolves.
Why Werewolf is Part of the Games Timeline:
Werewolf is a favorite at numerous game conventions and has been written about in several mainstream articles. Here are the other games I believe are the most culturally and historically significant games published since 1800.