NoiES is an NES emulator that I developed to teach myself how emulators work. I read tons of hardware documentation, but I was able to get the project to where it is now without looking at a single line of anyone else's code.
It's not perfect (yet), but most games with iNES mappers 0 through 4 should work. The PPU has some issues, but it's sufficient for most games. The APU is in a very early stage, but it does output sound!
Obviously there's no reason to use this emulator over any other NES emulator for the Switch. The UI has a file browser and that's about it. The accuracy is still subpar. If you want a flawless gaming experience you're in the wrong place!
Source code is available on GitHub. The main branch can also be compiled for Linux, and probably other systems too with some fiddling.