Hi!
Rootstock was renamed RSK a couple of years ago.
The RSK sidechain mainnet has been active since January 2018. The Beta testnet was active for two years without problems.
The currency in the sidechain is not called Rootcoin anymore (because some other alt-coin took that name). The coin is called Smart Bitcoin (SBTC) (but don't confuse with a new alt-coin self-called SuperBTC

that an exchange listed also as SBTC).
The RSK sidechain has a federated 1:1 peg with Bitcoin. In the future we would like it to become a drivechain.
More info in the RSK website
https://www.rsk.co/