I've seen almost every solution used internally at Amazon to one degree or another. It's really telling that you get a bunch of highly competent technical people in the room and they still end up fighting with the conferencing software and waste a bunch of time in the meeting trying to get everyone connected.

I'm really not surprised they built their own in the end. It's a clear pain point for companies.

That said, my current employers (not Amazon) have been using Zoom (zoom.us) and it seems to be really quite good. I've had almost no problems with it at all.