My guess is you're thinking of no$gmb, a very early Game Boy emulator:
replyhttps://gbatemp.net/threads/no-gmb-2-5-dos-full-version.6039...
I've got fond memories of using this to get a preview of Pokemon Gold before it was released in NA!
Found it
replyMetalNES, transistor level NES emulation https://github.com/iaddis/metalnes
While searching I also found a new one, VisualNES https://kaiokendev.github.io/nes/about
There is also one for GB https://github.com/aappleby/MetroBoy
See also Higan, formerly BSNES, which among other things is a cycle-accurate emulation of the SNES hardware and its enhancement chips (like the SuperFX used in StarFox/StarWing):
replyI'm not sure if this is the one you are talking about but I remember seeing this a little while ago.
https://mtmc.cs.montana.edu/
replyFound it
replyMetalNES, transistor level NES emulation https://github.com/iaddis/metalnes
While searching I also found a new one, VisualNES https://kaiokendev.github.io/nes/about
There is also one for GB https://github.com/aappleby/MetroBoy