Applications that rely on a central authority. For example, the current NFT artwork mania runs on a couple of centrally-operated websites. Once those sites go down, most of the URLs that those NFTs are linked to are going to stop resolving. It’d be way cheaper and environmentally safer to just use a centrally-operated RDBMS (disclaimer: I think NFTs and most cryptocurrency stuff is absolute bunk).
There’s Yacy. It worked ok when I was running it locally, but the moment I connected it to the rest of the network my search results were dominated by porn and spam sites.
the problem as I understand it is that with yacy you request relevant results from peers in addition to your own local DB. but that makes it really easy for spammers to keyword-stuff results and push their sites to the top.
I’m not sure how we can trust random people to give you search results without being overrun by spam.