Answer: The 64DD

When Nintendo knocks one out of the park, they really send it to the moon. The original NES system sold nearly 62 million units worldwide. Their followup system the SNES sold over 49 million units. Even obscure iterations and special editions of their Game Boy lineup sold millions.

When they’re hot, they’re hot. When they’re not, it’s painful. While many of us remember the marketing disaster that was the Virtual Boy gaming headset, the fact that we even remember the Virtual Boy means it did OK (even for a flop). The headache-inducing Virtual Boy still managed to have roughly 800,000 units shipped worldwide. Outside of collectors and video game trivia buffs, however, hardly a soul even heard about the ill-fated 64DD.

Although the 64DD, an add-on for the Nintendo 64, was announced even before the N64 itself launched, the product languished in the development phase for years. The add-on promised expanded game functionality including magneto-optical disks, online play, and a host of other features that would have been pretty darned innovative when the N64 was released in 1996. The 64DD didn’t hit the market until December of 1999, however, and by that time, the add-on was a whole lot too little, too late. It was released only in Japan and sold a meager 15,000 units before being discontinued in February 2001.