Making use of modern tool design, having adapters for modern file formats (e.g. the PNG file hadn't been invented back when the GameBoy was new! It would be several years later!), and outputting actual GameBoy roms that you can play on original hardware or emulators, now you too can make GameBoy games without needing to learn assembly language!
It's still in active development, and if you have a flashcart or similar device you can play them on hardware of your own.
"Re(1):GB Studio: make GameBoy classic games!" , posted Wed 21 Oct 12:33
Wow, RPG Maker but for an entire system, the most important handheld system ever made? This kind of takes chip music's idea of art through purposefully limited and/or nostalgic hardware to the next level!
When you think about the massive lifespan of the Game Boy and compare the primitive original games to later Pokemon and Rockman and Mario games that looked between FC/SFC quality, it's exciting to think about what people might make!