The original GEX firmware targets the STM32F072 microcontroller, which is used in the two custom hardware modules; you can see some of these in the photo below. In the future I hope to port it to STM32F103, and later to STM32F303 or others. A reimplementation for the ESP32 is also an exciting possibility, though it would be even more challenging.
The PC libraries were written and tested on Linux. The Python library should be portable to other systems, as it uses PySerial and PyUSB, but I didn't try it.