Most of the fiat-based stablecoins are based on UDS, with only a few being used extensively in trades. Here I am informing about 5 good but less popular USD based Stablecoins -
Stable USD (USDS)

It is issued by Stable Corporation, a financial technology company registered in the state of Delaware, USA. $USDS is available to trade with bnUSD and OMM tokens on the lesser known "Balanced" platform.
Origin Dollar (OUSD)

The #OUSD platform is based in the Cayman Islands, and is linked to NFT, DeFi, Lending, Investment. #OUSD is available to trade with USDT and BTC in KuCoin; it is also available to trade with USDT on Uniswap's (V3) and (V2) platforms.
mStable USD (mUSD)

It is created as an autonomous as well as noncustodial stablecoin. It is available to trade with USDT on popular exchange platforms like Hotbit and 0xProtocol.
Fei USD (FEI)

Released by software engineering Joey Santoro and his team on March 31, 2021, this stablecoin is based on the Fei protocol, this stablecoin is available for limited trade on exchange platforms like Bibox, Gate.io, ZT, Uniswap (V3), and MEXC.
Frax (FRAX)

Based on the open-source and permission-less ideas $FRAX is a fractional-algorithmic hybrid; it was developed by software developer Sam Kazemian in November 2020. $FRAX is available for limited trade on Gate.io, and Uniswap (V2).