[theocs]

They trade a token, sometimes called a stablecoin, that represent BTC as its underlying value.

Primarily two extremes for how this is done: Centralized, like WBTC (https://coinlist.co/help/what-is-wrapped-bitcoin-wbtc), and decentralized, like tBTC (https://defirate.com/tbtc/)

[codehalo]

Besides the extremes, there's the pragmatic in the middle - interoperability in general. RenVM supports Bitcoin and many other coins on multiple hosts, not just Ethereum (eg. Polkadot):

https://renproject.io

https://mainnet.renproject.io

[xur17]

I'm not convinced RenVM is really in the middle in its current state. Currently the core team holds all of the keys for the over $300M in Bitcoin stored by their project [0]. I'd take wbtc, which is held by a consortium of well known custodians in the space over that any day.

[0] https://www.theblockcrypto.com/daily/76787/ren-bitcoin-walle...