All of you know what I'm going to say..
Space Station 13.
Yes, it is a tile-based, laggy BYOND game, but you can do almost anything on there.
One time I almost killed a barman with a spoon to the head, and then with an energy sword conquered the research outpost by killing 6 people on it. Killing people and getting away with it is hard as hell to do on that game, so I hid in a locker, changed clothes, and got out scott-free.