Callisto Network is a blockchain platform with its own cryptocurrency (CLO) that is based on Ethereum protocol, so any Callisto improvements can be applied to Ethereum Classic. Callisto is NOT a testnet or a hardfork of Ethereum Classic. Callisto Network is developed by Ethereum Commonwealth, one of three ETC development teams.
Callisto is NOT a testnet or a hardfork of Ethereum Classic. This indicates that changes are made to the blockchain, or will be made in the future, different from the original.