Mafiascum is a community dedicated to playing online mafia. In its current form, the site dates back to 2003, and consists of a forum in which a handful of different mafia formats are played, and a wiki containing basic game information, rules of the house, and tips and strategies for new players.
When mafia games started running in GBS, several people either played on or knew of Mafiascum, and its wiki quickly became the jumping-off point for a lot of new players. Some concepts, like the Finger of Suspicion, lasted a few months but never really caught on; others, like OMGUS or WIFOM, were brought over wholesale and are still used today.
To date there have been two organized field trips to MS to make contact with the natives. The first, in 2007, established the SA Mafia Embassy, where everyone said hello and played for a bit and Xythar got his very own wiki page. The second, in late 2009, involved a handful of goons signing up for an MS game together and playing for a week or so before Alasdair showed up and trolled a bunch of people. The game mod freaked out, deleted half the thread, and permabanned everyone he could find associated with SA.
Every once in a while a couple people register MS accounts and play a game or two; registration is free and relatively quick, but be advised that games there tend to run excruciatingly slowly. 3-4 weeks to finish a single game day is common.