So I've built my own 8-bit computer from 4000 and 74HC series CMOS ICs. It has 4KB of RAM and is Turing complete. It has 16 arithmetic operations in its ALU and can perform conditional jumps. Programs are loaded by a BIOS module from a cartridge.
I was among others inspired by the work of Ben Eater:
https://eater.net/
/ @beneater
More information about the computer (including schematics and PCB layouts) can be found on my website:
http://maxbuegler.eu/#oss