libretro is an API that exposes generic audio/video/input callbacks. A frontend for libretro (such as RetroArch) handles video output, audio output, input and application lifecycle. A libretro core written in portable C or C++ can run seamlessly on many platforms with very little to no porting effort.
This is a companion discussion topic for the original entry at https://copr.fedorainfracloud.org/coprs/atim/retroarch/