If I'm not mistaken they don't offer Desktop apps and their browser experience has been just plain bad for me. Using Firefox on Linux I wasn't able to get mic and camera to work. While it did detect them just fine, it didn't allow enabling them. I tried that on multiple devices with the same result, so my take is that they consider Firefox as a second-class citizen.
I've had the opposite experience with a Mac - Whereby worked whereas Zoom just won't. Which means I'm forced to use the Zoom iOS app, sadly, because $work just migrated to Zoom because it can handle the (insane) video all-hands we have every Wednesday (with 20+ people).
I think whereby deserve to get more attention from the HN crowd, although the Founder did say they are working hard on the extreme interest for the past few days. So may be give them a few more days before a separate submission on HN.
I use Whereby every day and it's fantastic for small meetings. People don't have to install anything, just click a link and it works.