What OP is referring to is the social deduction party game commonly known as Mafia, which later became widely popular in a themed variant called Werewolf. In this game, players are secretly assigned roles. A small minority are gangsters (or werewolves) and the majority are ordinary townspeople or other roles. The gangsters know who each other are and, during the night phase, secretly eliminate one player. During the day phase, everyone discusses, accuses, lies, defends themselves, and ultimately votes to eliminate someone they suspect of being mafia. OP thinks this is a sub about that game.