Hash-based Signatures: An illustrated Primer
I think this focuses on the wrong reason for why signatures are important.  Sometimes, you can't or don't care to secure the channel you are using to communicate.  A signature doesn't hide the messages, so it is unsecured, but it does give a guarantee of who it came from.I know this is touched at the beginning.  But the odd shift at the end to "quantum will break all crypto" seems out of nowhere and makes this sound like a hypothetical tool.