What is the RADiuS? It's an Open Hardware Arduino-compatible shield for the easyRadio Advanced RF Module from Low Power Radio Solutions.

It's a fantastic RF/wireless solution. All you need is power, ground, and two serial-capable pins and you have reliable bi-directional communication between microcontrollers, desktops, laptops, or whatever. No frustrations over pairing, no twiddles with configurations, and it's approved for use in Europe, North America, and Asia.

This can talk to a Pi connected to a RADiuS-D in a snap, and there you have it, an inter-species communication in a matter of no time.

You can get more information here.