A 12 bit CPU (4 opcode + 8 data bits) based on a paper by Richard Eckert: "Micro-Programmed Versus Hardwared Control Units: How Computers Really Work", and enhanced with three hardware stacks (Data, Return and Keyboard).
It is still an ongoing project, so the software for it so far is a simple reverse polish notation threaded interpretive language, with work on an assembler in progress.

I think their use of “Tribble” is an apropos name for a 12 bit word.

http://www.mtmscientific.com/stack.html

Looks good. A indirect bit and 16 bits might be a good option for second computer design giving 4096
words of memory. Ben.

Thanks for the pointer to that paper:
http://www.cs.binghamton.edu/~reckert/hardwire3new.html

Byte magazine, Jan 1987 has "microcode versus hard-wired control" a 16 bit cpu.

Thanks - that's here
Microcoded Versus Hard-wired Control by Phil Koopman p235 (p255 of pdf)