I follow a page on Facebook called "Snes Forum" that posts a lot of Nintendo and retro content. Among them are mods for game systems and that's where I found this pretty little number.
A NES port made out of a NES cartridge. Not too shabby. You can find a lot of other neat mods on their page https://www.facebook.com/snes1forum if you scroll down enough. Among them a very nice looking Nintendo 64 portable mod.
Feel free to use this thread to post game system mods you've found or even some you made yourself, if any. And discuss the ones currently posted.