Certificate transparency (http://www.certificate-transparency.org/ http://www.certificate-transparency.org/) solves the real problem of allowing website owners

Certificate transparency (http://www.certificate-transparency.org/ http://www.certificate-transparency.org/) solves the real problem of allowing website owners to check that no one issues illegitimate certificates for their domains. I believe it is technically a blockchain although it doesn't have most attributes traditionally associated with blockchains (decentralized, PoW).