The PC-Engines APU2 is a very nice board when you need a lot more horsepower than a Raspberry Pi but still want low power, small form factor, and no moving parts.
Among the many features of the The APU2 are three LEDs and one mode button/switch.
I needed a device driver so that my code could control the LEDs and read whether the button is pushed.
I wrote one. It is up and available on the InterWorking Labs website: at https://iwl.com/.
Update: (February 2018): This driver no longer works on recent versions of the APU-2 board. However, there is a working alternative now available at https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=189772.