If you want to develop a program on Arduino with Raspberry Pi, then this tutorial has all the steps you need to take for it, in detail.

Before opening the Arduino software, wire up the Arduino according to the circuits page using the 8MHz minimalist breadboard circuit but with a 10k pull-up resistor on the reset pin (physical pin 1).

So just like with open source software, people can and do make derivatives of Arduino boards or entirely new products powered by Arduino technology. Why is openness important in hardware?

Arduino Shields, like the Xbee wireless communicator, aren’t compatible with the Esplora out of the box, but any existing Arduino software should work with the new pre-assembled controller.