Bitfinex, one of the best crypto currency exchanges available today. Bitfinex offers margin trading, lending and trading of various crypto currencies. ‘Finex is one of the highest volume exchanges. If you’re not trading any of your “blue chip” coins, make sure to use Bitfinex lending platform, probably the best available of all exchanges right now.
Bitfinex knowledge base – https://support.bitfinex.com/hc/en-us
No USA citizens allowed
They also have Ethfinex, an exchange based on ETH pairings