Ethereum Classic is an attempt at keeping the Ethereum blockchain unaltered by the part of the community that opposed the hard fork and the return of The DAO funds. It started trading on Poloniex and is getting more and more traction.
The Ethereum Classic mission statement is:
"We believe in decentralized, censorship-resistant, permissionless blockchains. We believe in the original vision of Ethereum as a world computer you can't shut down, running irreversible smart contracts. We believe in a strong separation of concerns, where system forks are only possible in order to correct actual platform bugs, not to bail out failed contracts and special interests. We believe in censorship-resistant platform that can be actually trusted - by anyone."
In 2017, the Die Hard fork was implemented in ETC, removing the Ethereum difficulty bomb. Currently, there are no plans to move to Proof of Stake like Ethereum, although developers at the IOHK institute are developing a new PoS protocol for Ethereum Classic.
* PoW: Proof-of-Work || * PoS: Proof-of-Stake || * PoC: Proof-of-Capacity || * PoN: Proof-of-Nature