Monero-Classic (XMC) is a hard fork of Monero (XMR), announced on 29th March. Part of Monero's development is that it hard-forks every 6 months, this is completely normal so not a surprise. After one of these scheduled hard-forks Monero retains the ticker symbol 'XMR' as well as the upgrades from the hard-fork; on the 6th April hard-fork it had changes including resistance to Cryptonight ASIC miners. If people disagree with these hard-forks, they can create their own versions of Monero. The strong financial incentives against this hard-fork, resulted in 4 different entities that each has created versions of Monero that still support ASIC miners, with their own new ticker symbols.