You've probably already heard of the Nintendo64 Wideboy's that are able to play either Gameboy Color or Advance games, well the Gameboy Advance version actually also plays Color games.
It's working pretty much like the Super Gameboy that was released for the Super Nintendo back in the day. The Wideboy's were not intended for consumers to use, but was a tool for developers and magazines to use.
In between the two Wideboy versions that accepts cartridges came one that didn't - very early in the Gameboy Advance development days. At the time GBA development kits were also in the early stages, the first
one was called a "TS2". I may not have the exact usage of the TS2 right, but this N64 cart was used to debug a GBA game in development and it would output content.
This thing is extremely rare though as the TS2 board only was available in limited quantities throughout year 2000, which is confirmed by a late 1999 manufacture date on the Wideboy AGB. After that time a lot of
TS2 boards were scrapped.
This wideboy has a history of being used to test a certain game for a developer based in the UK, no GBA cart existed at the time. They were having some "deep in game problems" and needed someone to iron out the bugs
and this was done by using a level select to play through the levels, and thereby getting the bugs to occur. So the UK company sent this Wideboy to a subcontractor to fix everything and once the debugging and fixing
was over the Wideboy was forgotten and ended up in a cupboard for a decade - the company never asked for a return.
Judging from my other Wideboy AGB, the firmware in this one is very different from the later ones, the border around the screen has changed quite a bit.
I remember having seen some screenshots from way back that had
this border... now if only I could find those screens.
Sorry bit that's all the information I have, feel free to correct my wrongs or explain it in detail, thanks :-)