Once upon a time in the land of Electronic Arts there was a little game development machine, and when I say "little" I mean "gigantic".  For you see, in the early 1990s EA scajummed together a development box known as the Sega SPROBE in order to produce their Sega Genesis titles.  In addition to behaving like a normal Genesis / Mega Drive, the unit allows for real-time analysis and debugging of titles in development.  ASSEMblergames has the story and plenty of pictures.

This quite sophisticated tool explains the prowess that EA had with Mega Drive games. Few in number and held close, these units are what made EA shine in the 90's. The unit powers up and plays games like a normal Genesis, however when switched into the bypass mode a variety of software options let you do all sorts of fun things to the [Genesis].

The speculation is that this SPROBE box is the kind of thing used when EA produced their unlicensed Genesis cartridges, making the SPROBE essentially a reverse-engineered Genesis development tool.  Also of note (and noted in the article's comments) is that this particular beast of electronics is Revision E in the SPROBE line.  This makes me wonder just how much more massive the earlier models in the SPROBE line had to be.  I have this vision of an ENIAC-sized computer that fills an entire room and needs extensive cooling all in the name of creating Budokan: The Martial Spirit.