My favorite for just being a straight up exchange but always can enjoy more users:

https://bisq.network/

No registration required or approval from a central authority
Peer-to-peer network
Decentralized arbitration system and security deposits protect traders
All personal data is stored locally
End-to-end encrypted communication routed over Tor
Multisig trade wallets
Fully open source

And of course once just a marketplace but now so much more..

https://openbazaar.org/

Like Bisq it is P2P, decentralized, has features for arbitration, Tor, open source, supports trading of over 1500+ coins

Bonus link Top 10 Decentralized Crypto Exchanges for a Successful #ProofOfKeys in 2019 https://hackernoon.com/top-10-decentralized-crypto-exchanges-for-a-successful-proofofkeys-in-2019-478dc38cff7a