A major chunk of Tether lives on Ethereum and is mostly being used for on-chain decentralized money-markets using smart contracts. (Eg Unisawp, MakerDAO, CurveFi and Compound)
Tether is issued on multiple blockchains. Omni is Bitcoin based, and recently most of it moved from Omni to Ethereum ($12.6 bil). Others include Tron ($6.4 bil), EOS ($90 mil), Liquid ($16.5 mil), and so on.
