custom library
Since everyone is posting custom libraries, I assume that was required somewhere in the rules? I’ll likely just use pygame, but if not, I might use this library or parts of it. I put the code on SF a few years ago, it uses Allegro and OpenGL: logo is here and code is here. It’s written in C disguised as Python (I converted it all from plain C after being inspired by pyplus).
It’s not ‘required’ per se. But if you want to use code that you made before the compo, you have to release it to everyone to use before the compo starts.