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.

Reserve Rights is an Ethereum-based stable token that is built on the Reserve Protocol. Reserve token will be initially backed by several other collateral tokens that are each tokenized versions of the US Dollar. The project has plans to transition to a collateral model that will not be pegged to the US Dollar.