The PiFace Digital plugs directly into the GPIO port on your Raspberry Pi and adds a whole load of input and output capability. You can detect switch states, drive motors, move actuators, blink LEDs... you know, all the good stuff! Program it any way you want but there's existing documentation for Python and Scratch! All of the input and output connectors are screw terminals, making it really easy to wire your Pi to all kinds of external systems. If you want to get an interactive project off the ground quickly with Raspberry Pi, the PiFace Digital is a great way to start.