6502
Weren't the Superboard 2 and Compukit UK101 6502 based (kit) single board computers that were around before the ZX81? Couple of guys had those at uni in the late 70s early 80s. Those were preceded by the KIM variants if memory serves correctly.
I went down the Z80 route and started work at a lab that had Intel MDS systems developing in PL/M for industrial controllers.