INK! is the smart contract language native to the Substrate ecosystem, written in Rust. Polkadot and its ecosystem, including present and future parachains, are deployed through Substrate. We use INK! for CryptoArena's Distribution Chain.
Solidity is the smart contract language native to the Ethereum Network, and is the most popular smart contract language of the world, featuring numerous protocols. We use Solidity for our CAT Utility Tokens.