But then you're basically describing normal currency backed by the nation state. The state can basically print its own money because it backs up its currency with state power - whether it be enforcing laws and governmental institutions, enforcing taxation to force citizens to use its currency, funding military defensive/offensive operations, provide various welfare services to citizens to create a safety net for the economy, and using monetary policies to modulate its growth. And every one of the activities I've listed above is achieved through human labor.

Obviously there is no nation that backs its currency value for an objectively "good" common cause - every nation probably only thinks within her interest for most of the time. If you want to create such an institution which can print money backed by the values you like - then the answer is much more political than technical, and the crypto algorithms alone wouldn't help you in achieving that.

I don't see the direct connection sorry. With currency, gold, etc, it can be stolen or controlled in ways a blockchain currency cannot.

I was merely talking about replacing proof of work with a human step rather than something computed. Intellectual labour (such as to plug our gaps in AI) moreso than physical. Answer a quiz when you buy a coffee or sit there for a few hours to mine coins while analysing a corpus. Something like that.

I saw that some exist, I don't know how relevant they are.

Why would anyone use such a system? For poor people the motivation is clear. However, who's going to contribute the resources required to make it run, if the whole point of the system is to disadvantage those with the resources?

> hopefully something generally useful to society at large

If it is useful then it won't be secure because it would be free to "hash". The mechanism has to be costly. Proof-of-work is in many ways proof-of-waste. If tomorrow we find out that hashing is profitable then everyone can start hashing and be able to attack the chain for free (subsidized by the usefulness). Only the hash power above the useful level can add security.

Gold?