I've heard that the Super NES was potentially compatible with the NES, in the same way the Genesis was backward compatible with the Master System. All it was missing was the cartridge slot. Sega offered one for the Genesis, but for whatever reason, Nintendo wasn't interested in following suit.
It turns out that the rumor isn't entirely accurate, but not as far off the mark as you might think. Here's what TT member RT-55J had to say on the subject:
|The 6502 processor, powering the NES,|
the Apple IIe, and surly robot laborers.
They might have been able to make it play Donkey Kong, but having it play all the games on this page (not an exhaustive list), or any game using more advanced mappers like the MMC3 (quite common) or MMC5 (Castlevania 3) would have required keeping far too much detritus from the NES's quirky design, which would have likely hamstrung the SNES's capabilities as well.
At the very least, NES -> SNES sourceports are relatively trivial from a programmer's perspective, as the 65816 was a successor to the 6502. Code relating to audio and raster effects would have to be heavily refactored, but that's to be expected.
There were a small handful of NES games ported to the Super Nintendo by hackers, but they're less demanding launch titles like the three Donkey Kongs and 10 Yard Fight, which had to be recoded for the format. You can test drive one of these hacks here, if you don't mind using your keyboard.
On a related note, there was a title for the Turbografx-16 (PC Engine in other territories) called 15-in-1 Mega Collection, which was actually a handful of games originally written for the VIC-20 home computer! They play pretty much the way you remember them... if anyone remembers the VIC-20 in the far-flung year of 2015. Which they don't, so forget I mentioned it.