Gold Bits Coin is developing a digital currency that is backed by gold. They hope to create a digital asset with less price volatility that can be used as a medium of exchange. GBC is built on Ethereum. Their marketing materials are unclear about how much gold they have in reserve to back each Etherreum-based token.

Tether (USDT) is the largest stablecoin cryptocurrency. It is pegged to the US Dollar. (1 USDT=$1 USD) Each Tether token that is issued is backed by $1 USD that is supposedly held in reserve. Tether has been the subject of some controversy because they have failed to allow a transparent audit of their currency reserves.
Tether facilitate transactions between cryptocurrency exchanges at a rate that is fixed to the United States dollar. This allows traders to take better advantage of arbitrage opportunities. Tether was created by the leaders of Bitfinex, one of the largest crypto exchanges.

Binance USD stablecoin is backed by US Dollars, and is issued in partnership by Binance and Paxos. The coin is approved by the New York State Department of Financial Services (NYDFS), and allows traders to convert US Dollars to a digital version without trading fees.