Embedded applications (for example, Arduino, BeagleBone, and Raspberry Pi) make heavy use of GPIO for reading from various environmental sensors (IR, video, temperature, 3-axis orientation, and acceleration), and for writing output to DC motors (via PWM), audio, LCD displays, or LEDs for status.
In v12.11 and later, a custom board called "DriveBoard" contains an ATmega328 SoC computer (replacing the Arduino) and all of the drive electronics with the exception of the two GeckoDrive modules and a BeagleBone embedded Linux computer which are attached to it.