An AVR USB joystick application.
Check out the branch for the specific hardware board revision. Master branch is likely not the right one to be looking at.
See the board in action at https://www.youtube.com/watch?v=7dX75QYCTEA
Board design files are available at https://github.com/stkerr/SU27-RWR-board. You need Eagle PCB to read them. I created the files with Eagle 7.7.