It's a really neat board. You can get kits from aliexpress etc. I wrote up some notes here https://www.philipzucker.com/td4-4bit-cpu/ . English descriptions are not so readily available.
Yesterday I proved the infinitude of primes, which I was pretty happy with. https://www.philipzucker.com/knuckle_primes/ A trivial theorem in the scheme of things, but one for which z3 certainly can't do it on it's own.
I also had some fun modelling the chips in verilog and model checking a verilog interpreter against them. https://www.philipzucker.com/td4_ebmc/ George Rennie got a similar thing working using the yosys toolchain https://github.com/georgerennie/philip_zucker_sby_demo