No, haven't seen anyone clone Bittorrent, but who would want to do that and for what purpose? Maybe the SecondLife currency (LindenDollars) would be a better example? Many companies want to have such a market where they can control the currency and its purchasing power and that's why there are so many MMORPGs. (FYI, I don't have a SL account and don't know the SL economy at all but as long as people want to pay 'real' money for your digital currency the business is worth a lot).