The company I work for is trying to come up with a product that basically operates to DO178B standard (we’re not using that term but that’s what we’re aiming for. Trains, not planes, but same sort of needs) and we just finished an operating system survey. We’re too small to write our own and are going with LynxOS.
And no, we didn’t consider Windows. No way we’d get that past the FRA.
A bunch of our stuff runs on LynxOS.