e.g. Pretty much any Concept2 rower you see in a gym or home that has been made in the last couple decades has a monitor that can provide realtime data to a computer via USB. I have one of these in my home that is older than Peloton but still connects to a computer just fine. If you actually have a Concept2 rower so old that it doesn't have USB, you can always upgrade the monitor (Concept2 sells upgrades).
The hardware has been under our noses for a long time, but it seems like we're only just now starting to make decent software to make use of it, although I'd say rowers are still a bit behind at present. It does seem like an under-served market.