“I'm a little confused, is this an ATS system that anyone actually uses?”

You read my mind. If the answer is “no”, then we can ignore this.

For one, if you go on to Hacker Rank's "Screen" page, they mention the product is used by Stripe/AirBnB/LinkedIn/Atlassian/IBM etc etc. I imagine that there's plenty more companies using it too.

But I'd also assume that their competitors are doing something similar so I don't think we as an industry can just ignore that it's happening.