The intended use-case is for bit-banging, i.e. sending electricity to places according to certain algorithms. Think about simple automation, like the control chip in your washing machine which executes the selected program by sending enable/disable signals to the water pump, valves, and the motor. Well, the same basic principles could apply to a lot of industrial processes and such, helping us rebuild the civilization.

It would also be really fucking great for helping post-collapse engineers do various calculations. Those chips are really slow by modern standards, but insanely fast compared to an abacus, a slide rule, and a sheet of paper.

BTW there's also dusk OS, which follows similar principles but is targeted for more advanced hardware, like the abundant x86 and ARM chips. It has a way more user-friendly interface, a basic GUI, filesystem drivers, and IIRC even networking capabilities, all possible to run on a PC from the early 90s. It also has great bootstrapping flow, allowing you to rebuild itself from source, flash itself to other computers, and flash Collapse OS onto microcontrollers.

Basically like a Linux install with all the dev-tools and sources already there, except much simpler, to the point that you probably can figure out how every component of the system works yourself, and fix issues when they happen. This knowledge will also directly translate into writing programs for collapse OS, because they share the programming language and many OS paradigms.