Quake 3 based 3D game engine
Quake 3 was an extremely popular game. And the best part about it was that they open-soured the engine. Lots of people figured out the engine’s internals and posted on the internet. The code was mostly C/C++ (which I found hard, at that time). So I made a ‘port’ of it in Visual Basic 6.0. It worked - but was slow enough to keep me from making actual game content for it.
If only I knew about Github back then.