uzics VS elks

The 8086 was (barely) capable of running Unix, whereas the Z-80 definitely was not.

https://github.com/chettrick/uzics

You're wrong ;-)

Neither the 8086 nor the Z80 have virtual memory. The x86 has a larger instruction set and address space (1MB) but as it turns out, early Unix kernels didn't need that much RAM either.

ELKS supported MMU-less operation on 8088 and 80286 machines, but I don't think an ARM port exists: https://github.com/ghaerr/elks

Roughly in the mid-90s I bought at a local surplus store a "Carry 1" industrial 8088 computer which to my surprise I later discovered it could run Linux (ELKS: https://github.com/ghaerr/elks). I ultimately sold it on Ebay because although it was a beautiful piece of old tech, I was struggling to find more space for other things.

Here's one. I had only the central unit, mine had two floppy drives.

I don't think you can replace the OS on these. Unless there is a way to boot them from DOS, but you are looking at 8c086 machine so the choice is limited. Linux or BSD won't work. But ELKS might if it can be made to boot from DOS. Minix 2.02 seems to work.

Yet ELKS works on 16 bit computers with 640k of RAM.

Some small size Linux-like OSes do exist though: one commenter suggested Lunix (which I didn't know, thanks for the link), and a slightly bigger one is ELKS which runs on old MMU-less x86 CPUs. I managed to run it on a 8088 industrial PC ages ago.

https://github.com/jbruchon/elks

I should have a Furby buried somewhere; now that I think of it, it may be the right platform to stick a bigger brain into, make it wireless so that it could be connected to the home IoT network then signal events or alerts.