I have been using the oldest of them all, BitShares DEX since 2016, before it was cool... some weird tokens that were only traded there got me into it... Fees are close to none if you withdraw or deposit via BitShares, but volume has plummeted compared to these overhyped exchanges built on top of ETH.
Now there's a fork called New BitShares riding the hype of decentralized exchanges. What a joke.