Bitfinex's decentralzied Ethereum-based cryptocurrency exchange ETHfinex just got a new "trustless" mode in which traders can participate in using only their wallets - no sign ups, no KYC, nothing of the sort.
All you need to trade on the exchange is your Meta Mask, Opera crypto wallet and ETH. It's still starting out so it has a few pairs - but shares liquidity with Bitfinex so it isn't hard to get your orders filled.