Freematics ONE uses a STM32 chip as co-processor to ATmega328p for access to data from OBD, GPS and communication module. If for some reason you want to update the firmware of STM32, here is a quick guide for how to do it.
Arduino Telematics Kits are designed to putting up a data logging and monitoring device with OBD-II, GPS and motion sensor data access. This users guide contains information to get start with the kit and the Arduino sketch designed and provided for them.
Freematics Vehicle Data Logger is a programmable device with OBD-II and GPS accessibility. Inside it is an AVR ATMega328P (compatible with Arduino UNO) and peripherals accessible with Arduino libraries including voltmeter, accelerometer, gyroscope, temperature sensor, microSD seat and Bluetooth (BLE and SPP) module.