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.

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.