The Golden Age of Open Protocols
This is micropayments, again.  There have been many, many micropayment schemes.  The trouble with micropayments is that all the enthusiasm for them comes from the people who want to collect them, not the people paying them.<p>One of the better ideas was micropayment email, as a solution to spam. You have to pay the recipient to get an email through, unless they&#x27;ve whitelisted you as a friend.  A centralized service could do that.  (One could see Gmail or Facebook doing that. LinkedIn already does. So do some dating services.)<p>Doing it in a distributed way is hard.  Blockchains probably won&#x27;t help; the cost of a Bitcoin transaction is too high and the network capacity is orders of magnitude too low for mail.  Local proof-of-work systems have been suggested, but never caught on.  (Probably not a good idea in the era of battery-powered devices.) Worth thinking about, though.<p>Urbit has a scheme where identities are anonymous but not free. That&#x27;s an anti-spam measure, because spamming results in negative reputation for a paid-for identity.  It thus make spamming expensive. Urbit is probably too weird to get much traction, but there are good ideas in there.