Stampery looks like a company that is dedicated solely to blockchain notarization. I am sure they do pretty much the same as the Bitnation notary, but "our" notary is completely open source and you could set up your own system if you want to use it for other blockchains. It is also free to use at this time. You do not even need to sign up and register to use it - but you are very welcome to sign up to the site as well!