Very interesting choice. I work on mission critical systems that aren't as mission critical as nuclear submarines. I don't think we'd ever consider anything other than an open source *nix.
When I said "mission critical systems that aren't as mission critical as nuclear submarines" I meant that a mistake can result in us losing $400 million in 30 minutes rather than the destruction of civilization as we know it.
I don't know what people in the latter case use, but it sounds like they use Windows for Submarines.
You write systems to autoplay Free to Play games?
Mistakes such as selling 610,000 shares at 1 yen, instead of 1 share at 610,000 yen.
Clash of Clans only makes on the order of ~$2M-$8M per day, according to estimates, so it'd be tough for a Clash of Clans outage to cost $400M. Only when playing with money, or with equipment worth $400M can you lose that much in 30 minutes.
(What kinds of equipment costs $400M and can be ruined in 30 minutes? Offshore oil rigs, I'm guessing. According to Quora, the least-expensive offshore rigs are $200M, while average is $360M. Ruining one of those with a software error would be a very bad day. Another option might be equipment in space such as satellites, though I imagine those are relatively harder to ruin.)
I think there is another side as well, software that may incur a liability if it fails due to loss of human life or recall costs. Eg bridge control, pharmaceutical QA, even electronic manufacturing (think Galaxy Note 7 design phase).
But Knight Capital did manage to lose $440 million in 45 minutes, due in large part to what I would call improper architecture and governance. So there you go. https://dougseven.com/2014/04/17/knightmare-a-devops-caution...
By the way, trading [should] have fail safes (i.e. stop after some amount of losses). A plane doesn't have fail safe, when the plane goes down, there is never enough parachutes =D
Solaris has had realtime capability for fifteen years, and most recently has been the embedded OS of choice for Sun/Oracle storage appliances. plan9 not being Unix (at all) nonwithstanding, Coraid's AoE products have used plan9 as an embedded OS in the past. Certainly in the recent past, US destroyers had embedded signal-processing systems built by a well-known HPC vendor running a derivative of INRIA ChorusOS. Green Hills Software's Integrity RTOS && development environment are also quite commercial, and have many successful deployments.
Any insinuation that military or embedded applications should be Linux (or Windows) deployments, or even necessarily free software, is ahistoric and, IMO, under-informed.