The RasPiO Duino is a small plug-on board for Raspberry Pi. It has similar functionality to an Arduino Uno, but is fully programmable from the Raspberry Pi. Once programmed, it can be removed from the Pi and used on its own. It can also be used interactively with the Pi. The Pi's GPIO ports are also broken out on the board as well. There's a 72 point prototyping area, with GND, 3V3 and 5V rails, where you can add your own components. As with other RasPiO boards, all the ports are clearly labelled and there are lots of options.

Each of the useful pins on the ATMega are broken out to a cluster of three holes. Male and female headers are provided, so you can connect whatever you like to your RasPiO Duino. RasPiO Duino is an easy, low-cost introduction to Arduino programming on the Raspberry Pi, and contains everything you need to start Arduino programming (as long as you already have the Pi).