Bitshares is pretty cool and operates as a decentralized exchange. Waves too.
Oh right, I totally forgot to mention the Waves DEx, its actually my favourite decentralized exchange that I've used so far!
Bitshares is also legit as far as I have read, I will dive in and check them out soon.
Another DEx is BitBay, this decentralized marketplace is actually a really great platform, definitely worth checking out.