An application layer, exactly. The specifics aren't well known yet
Hints about HAF come in blocktrade's posts, and he sometimes asks for public input and we get to see some cool documents to deep dive into. All of his recent updates will mention something about HAF, usually near the end. Hopefully, we'll see it in the wild in the coming weeks. I'd be surprised if it takes more than a couple of months from now for us to see it in action
Thanks. I'll go through his posts.