Besides proof-of-stake, there's also a coin that tries (tried?) a proof-of-work with greater public utility: Primecoin [1]. It creates Cunningham chains of prime numbers [2].
"Useful PoW" is a dead end. Good PoW functions require properties that rule out real world useful problems.
Wasn't there also like CureCoin that unfolds proteins for medical application?
Yes, and there's also SolarCoin which rewards users for producing renewable energy. The problem is that these coins are centralised, so while they may be very useful for what they do, they don't solve the same problem as proof-of-work coins which aim to be decentralised.
there is also gridcoin but they are not useful pow. they are proof of stake where the stake is the amount of contribution towards boinc projects and the likes, and they are affected by the oracle problem
Is that useful for anything other than the Primecoin?