In common it's the 3 axis + 9 buttons (6 physical + 3 emulated) with the PCB trace for Saitek's (or now Logitech) device.
Can be extented to a greater number of axis/buttons up to the free GPIO and ADC pins on STM32F103C8T6.
Firmware can be built using gcc arm toolchain. I've used gnuarm for win32 and Eclipse.
STM MXCube is the codegenerator for the MCU startup and default code. Caution: it likes to overwrite the existing code if you're not careful.