Yeah, look into SDRs if you haven't already. They are potential claims on freely usable currencies available to IMF members. Not a currency per say, but an asset reserve. Value is determined by a few of the economic powerhouse currencies of nations with ties to the IMF: US, Japan, Euro, Great Britain.
I have a problem with figuring out exactly what the SDR is. It seems member states have in advance agreed to on request exchange SDR's for a set of fiat currencies, up to a certain amount per country, more for the well standing coundtries. I guess that means it is a form of credit.
SDRs are utilized through the IMF, so only countries who have a relationship with the IMF (very few, but powerful ones) can partake. Post WWII, most foreign currencies are on a floating exchange rate. Countries that have poor exchange rates can "buy" SDRs from other holders or they can get them from IMF designation.
By having a basket of different currencies determining the exchange rate, countries with floating exchange rates that are poor stand a better chance to get better rates for their own currencies against the value of larger nations who's currency is higher value at that time.