Rootstock (RSK) is a smart contract platform that is connected to Bitcoin blockchain. In simple words it allows smart contracts on Bitcoin. This was Vitalik Buterin’s original vision before creating Ethereum. The goal of RSK is to add more functionality to Bitcoin by enabling smart contracts and near instant payments. RSK will have its own side blockchain with its own coins called Smart Bitcoin (SBTC) that can be convertible 1:1 with Bitcoin. RSK is still in its development phase and is not fully functional yet.