AirSwap is a Decentralized cryptocurrency exchange based in the USA. The exchange was launched in 2017. It’s reported volume is about 4.5-5 mln. $. The exchange provides peer-to-peer trading and has 3 available trading pairs and 6 coins.
Tether is a cryptocurrency launched in 2014. It is a so-called stablecoin currently leading by market capitalization. Although according to the initial idea, each Tether was backed by $1 (that was going to keep the price of Tether stable), the company not always managed to maintain this price (at some point in October 2018 the price dropped to $0.9 per one Tether). Tether succeeds in terms of market capitalization and its price is almost all the time is really close to $1.