Polymarket is in fact the oracle for all of the markets on their site. They don't host them in the sense that it's all on the blockchain. Augur has no actively

Polymarket is in fact the oracle for all of the markets on their site. They don't host them in the sense that it's all on the blockchain. Augur has no actively traded markets last I checked. It was good by the election but has been basically dead since. Polymarket has way more volume than Augur as of now. Omen is more decentralized but doesn't have much volume. There's also a version of omen on level 2 on the xDai chain.