Cartridges used for old, official tournaments known as Nintendo World Championships and given to winners as a prize. Apparently, there are only 116 copies ever made. The cartridge itself contains Super Mario Bros, Rad Racer (Square) and Tetris.
And one of these is currently put onto eBay, with the bidding price at 100 000 USD.
The sale never went through it was a sham bid, I know the seller on another site. There's more than 116 copies, I think it's somewhere around 340 if I remember correctly. These carts generally sell between 8-12k in good shape the one that was listed would have been lucky to make it's opening bid of 5k realistically. Three or four of these sell per year on average. There's a gold version given away by Nintendo Power that sells for around 20k or more but there's only 30~ copies of that version. I'm not sure how this one got so blown out of proportion or how it got so much media coverage but it was just a bunch of trolls on the internet perpetuating a scam. Although one good thing did come of this it's brought other copies of rarer games out with people looking to make a quick buck.