nanoarch
nanoarch is a small libretro frontend (nanoarch.c has less than 1000 lines of code) created for educational purposes. It only provides the required (video, audio and basic input) features to run most non-libretro-gl cores and there's no UI or configuration support.
Building
Other than make, pkg-config and a working C99 or C++ compiler, you'll need
alsa and glfw development files installed.
Running
./nanoarch <core> <uncompressed content>