RSS (RDF Site Summary or Really Simple Syndication) It is in use a fair amount, but it is usually buried. Many people don't know it exists and because of that I am afraid it will one day go away.
I find it a great simple way to stay up to date across multiple web sites the way I want to (on my terms, not theirs) By the way, it works on Lemmy to :)
Honestly there is rarely a blog I want to follow that doesn't have it. I do think it would be great to have more readers using it so that it becomes more significant, but for my reading it is actually pretty great.