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I think you are missing the point. You might not have access to any modern hardware + modern, multi MLoC operating system medium/ftp server/whatever to boot in a post-apocalyptic world. This would at least provide some level of computation on simple devices.

Even if you do have access to a modern computer which is not fried, you still need a whole bunch of devices, mass storage stuff and mains electricity to be able to boot it, and then on to find and boot some software.

The OS above would run in things like graphing calculator cpus, 8-bit video games and other "almost non-computer" devices which actually have simple but useable CPUs. It would be better than going back to the 1900s.