Tether is extensively used in Crypto markets as an alternative for US Dollar. All the Trading Platforms would facilitate the exchange market with Tether Pairing along with Bitcoin Pairings.
Tether is originally designed to be always equal to 1$ (USD). Therefore, Tether is obviously a Stable Coin.
Ticker Symbol in Market for Tether is "USDT" (stands for US Dollar Tether).
It successfully managed its price balanced on par with 1USD always (with insignificant and negligible fluctuations in price).
Tether was developed by Tether Limited Company and it had faced many legal issues by US Government due to various reasons.
You can see the Live Chart for Tether maintaining a constant value fixed to the price of USD: