You ever just nerd and make a completely fictional 8-bit microprocessor? Sometimes a crux does.
Harvard architecture, two general/accumulators, a memory pointer. Has space for 256 bytes of ROM and 256 bytes of memory.
The program code does a short Fibonacci sequence after copying a reference into memory.

@RubySqueakbird
8 bit?

I'm on the third iteration of a DIY 16 bit RISC machine with 24 bit address space and full von Neumann architecture.

Which I plan to actually build in 74 TTL.

@MeiLin All 8-bit, yep. Not even any 16-bit address busses or things. :>
@RubySqueakbird @MeiLin you can choose arbitrary address bus length, it may be 13, it may be 509 :D