zkSync is a scaling and privacy engine for Ethereum. It is built on ZK Rollup architecture. ZK Rollup is an L2 scaling solution in which all funds are held by a smart contract on the mainchain, while computation and storage are performed off-chain. For every Rollup block, a state transition zero-knowledge proof is generated and verified by the mainchain contract. This includes the proof of the validity of every single transaction in the Rollup block. Additionally, the public data update for every block is published over the mainchain network in the cheap call data.
zkSync currently supports only transfer of ERC20 tokens using their scaling solution and smart contract functionality is in the roadmap for 2021. They don't have a token yet.