The Elements of Computing Systems is the book behind nand2tetris. I’ve done the course a few times on Coursera. The astro-8 (the computer in the video from this post) uses microcode in the CPU but nand2tetris just uses instructions whose bits directly drive the cpu. Although I do like how nand2tetris shows how layers of abstractions can be arbitrary, and even simpler than they are usually done in the real world, and you can still build on top of them using additional layers of abstractions. Even in the first step, instead of using different gates you only use nand and then create the needed logic gates from that. And the machine language it uses is at a microcode level and you build a stack language on top of that. (And then build an Java like language on top of that.)