Considering the 50 year anniversary of lunar landing, I thought it might be fun to share the following bit of information:
https://github.com/chrislgarry/Apollo-11/
It's the original Apollo 11 Guidance Computer source code for the command and lunar modules. It's written in AGC assembly language.
https://en.wikipedia.org/wiki/Apollo_Guidance_Computer
The original system apparently didn't use any OS, but I wonder whether they'd use Linux today. Btw, Linux is the scientific community's operating system of choice. CERN's Large Hadron Collider is controlled by Linux. NASA and SpaceX ground stations use Linux.