I would just prototype with a centralized database-backed system, if you don't need anonymity (and for this, non-anonymity might actually be an advantage). Thi

I would just prototype with a centralized database-backed system, if you don't need anonymity (and for this, non-anonymity might actually be an advantage). This isn't an interesting technical idea, it's interesting because of the social/economic/etc. behaviors, so I'd try to do the cheapest/easiest/oldest technology possible. More like a PayPal-style system...which ironically actually started out as a "digital currency" system on handheld terminals before they rolled it back to an email/website thing.