That's what ya call the basic game system. It's owned by Wizards of the Coast but we can use it under their Open Game License. Dat way, it'scompatible with other games usin' the same system. You make characters, in this case, wiseguys, babes and made guys. Each character has numbers that represent their various attributes. These numbers are then translated into modifiers and whenever you gotta do somethin' that might fail, you roll a 20-sided die, add or subtract the modifier and then check the result. Yeah, I know it sounds complicated, but it's not. Anybody who plays a role-playing game can tell ya how ta play.