This is a project of mine which contains a working, self-hosting, Forth interpreter for a single instruction machine. The instruction is called "SUBLEQ", short for (SUB)tract and branch if (L)ess than or (EQ)ual.

Everything has to be synthesized from that instruction, bitwise operators have to be implemented in terms of repeated subtraction and self modifying code used to create indirect loads and stores. In doing this it is possible to port a working language that is capable of generating new images for the machine.

It's possible to play with it online at:

https://howerj.github.io/subleq.htm

(feedback welcome)

The Forth is fairly feature full and includes cooperative multitasking.