dYdX
Summary
dYdX provides a way to trade derivatives on Ethereum.
Users of the protocol can trade with margin, which allows them to short any ERC20 token or buy any token with leverage. Opening a position requires taking a debt. Therefore, a margin trader will need to find a creditor who will lend them the required tokens. Users negotiate via relayers or in private, then settle on-chain once they agree on terms.
dYdX also plans to support options trading. Options give a right to its owner to buy or sell an asset in the future at the specified price. It can be used as a speculation or a hedge.