Bung Enterprises ltd. is a
Hong Kong company that produced
devices for
game consoles, most notably
development/
back-up units like the
GB Exchanger for the
Game Boy and the
Game Doctor/
Professor SF series for the
Super Nintendo/
Super Famicom.
You can load these devices with ROM data and connect them to your console, where they will simulate a game cartridge. This made them cheap alternatives to Nintendo's official development kits. Of course, they could also be used as tools for piracy.
Eventually, Bung were sued by Nintendo and had to shut down their operations, so their devices are no longer available.
Their website is still online at the time of writing, at
http://www.bung.com.hk.