It's an open-source project and not a startup, but I think that Namecoin [0] is a very interesting non-currency use for blockchains.
It is a decentralized name registry that maps domain names to public keys and IP addresses, removing the need for Certificate Authorities and resolving Zooko's triangle [1].
I do agree that blockchain is insanely over-hyped, has very few real use-cases and mostly used as a PR tool in ways that makes no sense. Sound money and cryptographic identity registries are among the only reasonable use-cases that I can name.