A (shitty) Snake clone for GameBoy written in C with gbdk. This should a decent start point to code something with gbdk.
Take a look at awesome-gbdev, a curated list of awesome GameBoy Development resources, tools, docs, related projects and open-source ROMs.
Compile with gbdk
bin\lcc -Wa-l -Wl-m -Wl-j -DUSE_SFR_FOR_REG -c -o quadratino.o quadratino.c bin\lcc -Wa-l -Wl-m -Wl-j -DUSE_SFR_FOR_REG -o quadratino.gb quadratino.o
or download the ready ROM (may not be the latest build)
Reccomended emulator: bgb