Gambatte is an open source Game Boy/Color emulator. The accuracy of the emulator is among the highest and is based off numerous reverse engineering tests and document studies. It is currently available as both a core for RetroArch, as well as an individual emulator. It used to be used in the Super Game Boy component of Higan. Nowadays it's not actively developed anymore and while it has great accuracy, it doesn't support many additional features like Super Game Boy emulation.