About Ethereum Classic:

Ethereum Classic can be called an “artificial cryptocurrency” because created by an attack of hacker on June 17th 2016. Millions of Ether around the value of $50 million were stolen that day. ETC coin forked to a new chain to repair the damage caused by the attack. On 21st December 2017, Ethereum Classic had its own ATH (All-Time High price), which was equal to 48 USD.

Resources:

Official website: https://ethereumclassic.org/
Whitepaper: https://ethereumclassic.github.io/assets/etc-thesis.pdf
Source Code: https://github.com/ethereumclassic/