A Hundred Stars
It may not sound like much, but one of my GitHub repositories recently passed the one hundred star mark. It's not the one I'm most proud of, but the one that seems to be the most useful to other developers: GBA tests. I wrote it along with my Game Boy Advance emulator eggvance to verify its CPU implementation. I tried to cover as many edge cases as possible to eliminate the chance of something misbehaving, because finding such a thing will drive you crazy. It was a much nicer experience to work on other parts of the system without the possibility of a CPU bug lingering in the back of my mind.