(I am providing a different answer, not building on the prior one.) Tether is a centralized financial service which mints USDT in exchange for USD and lets you redeem USDT later for USD (using fiat bank wire transfers in and out, taking a small but non-negligible cut in both directions, and so $0.9987 or somewhere around there is the true power bound target of the currency, not $1.00). Honestly, I am not sure how their service is legal in the US under merely FinCEN regulations (the ones that prevent you from selling large prepaid gift cards and redeeming them for cash), OFAC aside...