I see SKM has PoA - but what does PoA actually mean? Proof of what?
It stands for " proof of authority " which is a consensus mechanism for blockchain and an alternative for proof of work, proof of stake. There are many companies that used like Ripple. If you are interested in understanding the concept deeply, just search for it on youtube, there are some cool video about the subject.
This type of consensus is becoming more common, I saw projects like Gochain using the mechanism but I think it's not that decentralized than POW or POS because only choosen companies can mine it.