Made this super-minimal (~13Kb) app/platform layer(s) lib:
https://github.com/HardCoreCodin/SlimApp
No dependencies on anything (not even any standard library stuff).
Can compile in either C or C++. CPU-only (no OpenGL).
Very beginner friendly, leaner and smaller than other alternatives.
Currently only implemented win32 for the platform layer, but app-layer is completely decoupled.
(Documented by examples - check'em out to see if you like it)