A few years ago I bought a "retroshield", which is the same kinda idea:

http://www.8bitforce.com/projects/retroshield/

There were (are?) boards for driving a Z80, 8085, and a couple of other processors all via an Arduino-Mega.

It was a fun project which later lead to me working on a simple single-board Z80-based system, and that lead to me playing around with CP/M and similar things.

Some years ago there was Pinguino (penguin in spanish). Pinguino is an Arduino-like board based on a PIC Microcontroller.

But it is dead: https://web.archive.org/web/20180512095336/http://www.hackin...