BGB is an emulator/debugger for the Game Boy, Game Boy Color and Super Game Boy systems. The goal of BGB is to try and provide an accurate emulation of the hardware.
This is to try and be an emulator that is not only good at running a multitude of games as how they would of on the original system, but also makes the emulator a powerful debugging tool. Thanks to its attempt at accurate emulation, it also means the emulator has an exceptional compatibility with games.
The emulator also has the added ability of being able to use the game link functionality over the Internet. Allowing two users to link their consoles no matter where their located.