There is a decentralized stablecoin, DAI that's backed by Ethereum holdings and smart contracts. I think if ETH is doing ok you can swap a DAI for $1 worth of ETH. If it ETH crashes I presume you get given the ETH which you can sell. It relies on 'oracles' to give the ETH/USD exchange rate to the smart contracts. https://medium.com/@james_3093/the-dai-stablecoin-is-a-game-...