Raspberry Pi is an ARM based, credit card sized computer. In addition to the usual computer features, it has two GPIO ports with a total number of 21 pins that can be set (on / off) or read. Moreover, one of those pins can be used as a PWM output. Thus, it can be easily connected to sensors, actuators, relays and so on to operate them.
A driver for INDI-for-Java is available to allow easy contorl control of these pins within any INDI enabled software.
This driver is not include with official INDI Library. It requires INDI4Java server.