The Game Boy is a handheld game console developed and marketed by Nintendo. It was released in Japan on April 21, 1989, in North America on July 31, 1989, and in Europe on September 28, 1990. Nintendo's first handheld to use ROM cartridges, it succeeded the Game & Watch line of handheld electronic games and competed with Sega's Game Gear, Atari's Lynx, and NEC's TurboExpress in the fourth generation of video game consoles.

https://github.com/gbdk-2020/gbdk-2020
An updated version of GBDK, C compiler, assembler, linker and set of libraries for the Nintendo Gameboy, Nintendo Entertainment System, Sega Master System, Sega Game Gear.
https://github.com/mrombout/gbdk_playground
Simplified GBDK examples