Town of Salem
Town of Salem is a browser-based game that challenges players on their ability to convincingly lie as well as detect when other players are lying. The game ranges from 7 to 15 players. These players are randomly divided into alignments - Town, Mafia, and Neutrals. If you are a Town member (the good guys) you must track down the Mafia and other villains before they kill you. The catch? You don't know who is a Town member and who is a villain. If you are an evil role, such as a Serial Killer, you secretly murder town members in the veil of night and try to avoid getting caught.
basically you -- as a town, lynch everyone who isn't town, by voting. just try to figure out clues, like if you're a sheriff you can see who's mafia at night and etc, but don't reveal your role or the mafia or neutrals will kill you. neutrals are witches serial killers werewolves and arsonists. and survivors, who win with everyone. check the wiki if you want an in depth analysis, but i jumped right in and figured it out after my second game
this quick tutorial is also good