Being a layer 1 blockchain network, Harmony will support a number of decentralized exchanges (DEX). We can expect to see more DEXs support and run on Harmony as the network matures.
On March 2nd 2020, the decentralized exchange ViteX listed ONE tokens for trading. ViteX supports (1) on-chain order matching and (2) smart contract-ebabled transaction fee collection and distribution of dividends. ViteX is powered by its own token (VX).