Lottery Bond

Lottery bonds are government bonds that are raffled off monthly. This system is prominent in the United Kingdom, issued by United Kingdom's National Savings and Investment (NS&I). These bonds don't pay interest, and have no guard against inflation, but hey, the winnings are tax free. They sell at a discount to par, like a T-Bill in the U.S., and the amount of discount, metered by the duration to maturity, gives an imputed interest rate to those lottery bonds.

Good luck.