One of the earliest NES emulators for MS-DOS called LandyNES was presumed missing for years, thanks to the FTP servers it was hosted on becoming defunct.
However, a Twitter user named WaluigiBSOD recently posted on the social media site that they had managed to unearth the emulator on an old CD-ROM ISO named "HaCKeRz KrOnIcKLeZ". This is a CD-ROM containing hacks, guides, bots, and cheats, as well as emulators for playing Sega, Nintendo, and Atari games.
Using an experimental file-browsing website called Discmaster, WaluigiBSOD was able to explore the contents of the old CD-ROM and that's when they came across this remarkable find.
Bizarrely, it appears that, although the discovery happened just this month, the ISO containing the emulator has been widely available online ever since June 30th, 2020. WaluigiBSOD even got it to work, showing some images of Donkey Kong, running inside of DOSBox. They posted instructions on how to get it to run inside an NSO file available from the above link. You'll need an NSO reader to be able to access these.
According to WaluigiBSOD, the most recent Windows OS that can run it are Windows XP and Windows Server 2003 32-bit, though those are pretty unstable compared to using a third-party program like DOSBox.
As a brief history lesson, Alex Krasivsky (better known as Landy) was developing LandyNES in the mid-90s, at a time when there were only a few Japanese NES emulators that had been shown to the general public. It later served as the basis for iNES, which popularized the ".nes" format in ROMs, as the iNES creator Marat Fayzullin briefly worked with Krasivsky before deciding to splinter off and develop their own emulator for the system independently. It's a remarkable find, and a great way to start off the year.