Fitlet GPIO Connector User Guide
From fit-PC wiki
fitlet GPIO interface provides easy and convenient way to operate external devices without the need to open the box, solder wires and designs special hardware. The interface accessible from fitlet's back panel connector via 14-pin ribbon cable (sold as accessory).
fitlet GPIO Software Development Kit (SDK)
The section provides all the necessary information and resources in order to operate fitlet GPIOs in your own setup, under either Linux or Windows environments. SDK includes relevant drivers, API libraries, explanations and examples.