The Atari 2600 wasn't the very first system ever made, but it's certainly the poster child of the golden age of home video games. But its reign didn't last forever, and eventually the Nintendo Entertainment System became the king of the consoles.
Much of the NES’s early success is primarily due to Super Mario Bros. It was the one single game that made everyone finally forget the 2600, as well completely write off the 7800.
Though 28 years later, those who have been faithful to Atari's ancient platform can finally nab the one game they've long dreamt of; a Super Mario Bros port for the 2600.
It's a homebrew effort from Chris Spry, one that's called Princess Rescue. But we all what it's supposed to be (and most seasoned 2600 players know that the vast majority of its games were supposed to be something else).
Given the age of the hardware, which made its debut in 1977, Princess Rescue is actually quite well put together. Again, this is a real game, which comes on a real cartridge. Which is available for $30, through Atari Age.
By the way, another oddball Super Mario Bros port, but one that was officially sanctioned by Nintendo, and which shares more than a few similarities than the unofficial effort, is Super Mario Bros Special. Created by Hudson Soft for the Japanese NEC PC-8801, hardcore Mario fans consider it the true sequel Super Mario, since it actually predates Super Mario Bros 2/Lost Levels.