Zach Barth and his former studio Zachtronics released several entertaining puzzle games based on idealized fake assembly languages. These are a lot of fun and useful for introducing registers and multiprocessing.

I keep coming back to the idea of taking that concept and just running with it, IE building up a toolchain alongside some concrete tasks to solve with it and just adding more detail until we reach a reasonably sophisticated level

I've been staring at 0x10c, carwars and battletech and there's a sense that I could build a sort of programming / engineering Zach like