What are the "risk-free" investments?

Issuer:Government of Singapore.

Typical issue size and maturity
S$2 - 3 billion for benchmark bond issues
S$900 - 1,000 million for Treasury bill (T-bill) issues
The maturity ranges from 3-month to 15 years with 3-month and 1-year benchmarks for T-bills and 2-, 5-, 7-, 10-, 15- and 20-year benchmarks for bonds.

Typical denomination
S$1,000 for bonds and T-bills

SGS Bonds
SGS bonds carry a fixed semi-annual coupon paid on the 1st and 15th of the particular month. In case of holiday, coupon payment occurs on the next business day.
Coupon accrual: Interest accrues from the previous coupon date (inclusive) to the settlement date (exclusive).
Ex-coupon date rule: SGS trades ex-coupon three working days prior to the coupon date.
SGS bonds are non-callable/non-puttable bonds with bullet redemptions.

SGS T-Bills
SGS T-bills are zero-coupon, and issued and traded on a discount basis.

source: www.sgs.gov.sg

My comments:
SGS bonds and T-bills are risk-free unless the government defaults. The SGS bonds, in particular, provide a constant (fixed coupon rate) and regular (half-yearly) stream of income. However, given the ultra-low interest rate environment, do you want to put your money in these instruments? The yields are not even enough to beat the inflation. So are they still "risk-free"?