Comment by d3Xt3r

In addition to Photon, I would say QNX itself (the desktop OS). I ran QNX 6 Neutrino on my PIII 450 back in the day, and the experience was so much more better than every other mainstream OS on the market. The thing that blew me away was how responsive the desktop was while multitasking, something Linux struggled with even decades later.

Similarly, I'm also gutted that the QNX 1.44MB demo floppy didn't survive past the floppy era - they had some really good tech there. Imagine if they pitched it as a rescue/recovery OS for PCs, you could've run it entirely from the UEFI. Or say as an OS for smart TVs and other consumer smart devices.