I've only been vaguely following cryptocurrency for the last few years after messing with it a while back, but I think the Ethereum Name System should count as

I've only been vaguely following cryptocurrency for the last few years after messing with it a while back, but I think the Ethereum Name System should count as one of your 3 requested compelling cases. Trustless, decentralized DNS with pretty much perfectly fair auctions. No messing with registrars, or having it taken away or censored by a government, or being front-run by GoDaddy. It was always one of the coolest uses I saw, and an example I always give to explain why smart contracts are useful. https://ens.domains/ https://ens.domains/