Ethereum Classic (ETC) is not an original cryptocurrency, but rather the older version of Ethereum (ETH). It all began with the DAO fiasco in 2016 and the need to bring changes in the Ethereum blockchain, leading to a hard fork. The people who were against the hard fork supported the original Ethereum, which was later renamed Ethereum Classic, and the upgraded version or the hard forked version, (ETH) Ethereum.
Ethereum Classic is an open-source, decentralised blockchain technology platform possessing smart contract functionality. Much like Ethereum's blockchain, Ethereum Classic's blockchain is quite similar too, with the exception emerging from block 1920000. Also, Ethereum Classic uses the proof of work protocol instead of proof of stake, which is used by Ethereum and many other cryptos.