And Web Rings. In fact, I'm surprised considering how ideas simply get recycled (IRC -> Slack) that nobody has tried to reinvent the web ring. I suppose it's the death of self hosted sites that has killed it.
In most contexts they’ve been replaced by AI driven recommendation engines.
Although I discovered a delightful example of a human curated recommendation engine the other day in the form of bandcamp’s `Recomendations` feature :)