This is marginally useful, but I wrote a small ‘subleq’ playground — it’s an instruction set with just one instruction, “SUBtract and branch if Less-than or EQual to zero”.
https://github.com/incanus/subleq
It was fun to see how simple a model of computation could actually be.
Some people wrote a Forth interpreter on top of that.
Oh, this is totally also my jam. Will dig some of those up.
gopher://hoi.st has nice stuff for subleq and awk