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.

HUSD token is a stablecoin that was created by a Hong Kong based company called Stable Universal. HUSD is backed by US Dollars in a 1:1 ratio that are held in a trust company. The HUSD stablecoin is designed to have a governance structure that will increase security, liquidity, and transparency. Monthly audits of HUSD's reserves are conducted by an independent accounting firm to ensure that the 1:1 backing is maintained.

The Multi-Collateral DAI stablecoin uses multiple types of collateral to back its value and an interest rate mechanism to stabilize its price. It is designed to be a digital currency with a stable value. MakerDAO is the decentralized autonomous organization that manages DAI and works to combat its price volatility. Multi-Collateral DAI was launched in November, 2019 and is meant to be a successor to the Single-Collateral DAI, that will eventually be phased out. The new stablecoin will enable new features to the Maker Protocol, such as the the Dai Savings Rate (DSR), as well as additional types of asset collateral.