PC gamers of a certain age probably fondly remember the Commander Keen game series, some of the first smoothly scrolling platform games made for MS-DOS. What many classic gamers might not know is that before working on Commander Keen, John Carmack, John Romero, and the rest of the team at id Software (then known as Ideas from the Deep) pitched Nintendo on the idea of porting Super Mario Bros. 3 to the personal computer. The group went so far as to code up a proof-of-concept demo for the game running on the PC.
As David Kushner memorably lays out in his book Masters of Doom, the IFD team managed to come up with one of the first smooth side-scrolling algorithms designed for the PC way back in September of 1990. Unlike platformers on dedicated game consoles (which had hardware more suited to smooth scrolling), PC side-scrollers at the time usually had clunky, screen-clearing transitions when a character got to the edge of the screen. Carmack's algorithm, though, allowed for much smoother background movement by only redrawing the elements of the screen that actually changed frame to frame.
After proving the concept with an SMB3-like one-level demo called Dangerous Dave in "Copyright Infringement," the team set down to make a respectable PC conversion of Super Mario Bros. 3. They sent it to Nintendo in the hopes of gaining a lucrative licensing contract, but Nintendo declined the offer (Romero says they weren't interested in making games for non-Nintendo hardware anymore). At that point, the tech was funneled into the Commander Keen games. Id Software later went on to focus on leaps in 3D gaming with Wolfenstein 3D, Doom and its progeny, and the rest is history.