Gaming Educational game where you design your own CPU?

[StackMasher]

Like this: http://store.steampowered.com/app/576030/ but for free. I would just pirate that game but I can't find it anywhere so I'm looking for alternatives.

 

[Originality]

I've not heard of many examples of that outside of Minecraft and its derivatives.

 

[FAST6191]

xkcd because why not
https://xkcd.com/505/

If you just want to go a step beyond a few logic gates and adding machines, which any old electronics CAD/simulation program can probably pull off, then you could download a FPGA simulator. Likewise there are fully decapped chip specs out there in the world, relevant as of that


Many people find emulating a chip8 a useful thing http://devernay.free.fr/hacks/chip8/C8TECH10.HTM . it is not necessarily a game but the end result will allow you to play several games as a result of working through the logic of a chip.

Likewise a learning exercise for many programmers starting on assembly is the so called y86 (a very simplified version of an older x86 chip) http://www.cs.utexas.edu/~hunt/research/y86/y86-asm.lisp

Any truly modern stuff is probably handled by modules being designed, and probably a lot of help from evolutionary computation if various talks I have seen are anything to go by.

Another approach you may enjoy is building a disassembler for an unknown machine