Thank goodness for modders, Without them we wouldn't be able to take one awkwardly shaped gaming system and cram it into another one in order to make it portable. Case in point is this mod from Evil Nod where he has placed a Nintendo 64 inside a Game Gear. Years ago I would have made a Sega/Nintendo wars joke here, but with Sonic all over the Wii and DS the time for jokes like that has clearly passed.
What is truly impressive is that the thing is entirely portable. Not content with simply cramming the N64 inside the Game Gear, Evil Nod also worked in the N64's controller as well to create an entirely contained system that he calls the N Gear 64. Sadly, the Game Gear, my portable of choice as a child, is still a massive hunk of plastic and shoving a N64 cartridge into definitely doesn't make it any sleeker.