Assuming you want ID verification, why would you need a blockchain? Your identity is deeply linked to who you are and we have identity documents and trusted entities to provide them. These entities can absolutely act as a third-party to verify who you are. This can happen with several different parameters: whether your identity is provided to the site you are using, whether the site your are using is known to your identity provider, whether identities across sites are identical or only linkable by the trusted party. But in all those examples (that are currently implemented by some countries), blockchain is not a requirement.

Assuming you don't want actual ID verification, the choices are even larger but with different trade-offs.