And let's not forget Maltron:

https://www.maltron.com/store/p20/Maltron_L90_dual_hand_full...

It looks ugly, but they were the original inventor of contoured keyboards I think.

I've had one for many years. It's my least favourite keyboard. As they rent them out, I would suggest trying one before buying, if possible.

Part of my dislike might come from the MX Black switches they used at the time, and I gather that alternatives are available now. Another factor is their keycap profile and the placement of the switches, which mean that if your fingers get misaligned, you hit a gap between the keys. This is more irritating than it sounds.

While not a criticism at the time it was built, it's also worth noting that there was (and is, I think) no layout customisation other than a choice between fixed layouts with a couple of switches on the underside of the keyboard. The case is vacuum-formed, which looks and feels cheap compared with modern competitors, and the bottom is glued on which would make repairs difficult (not that mine ceased to work).

and https://bastardkb.com