panStamp is an open source project created for the enthusiasts interested in measuring and controlling things wirelessly. panStamps are small wireless boards specially designed to fit in low-power applications, simple to program and simple to work with. They allow for direct connection with your sensors to make then available wirelessly. panStamps are NOT WiFi modules. They are wireless boards which run a compact stack and communicate with each other using a protocol called SWAP over 868/915 MHz using Texas Instruments CC1101-based radios.
panStamps are Arduino clones so existing libraries should work as well.
Details about architectures, protocols, stack, libraries and applications can be found on the documentation wiki. The project’s source code can be found here.
I have found more information in: http://www.panstamp.com/
This project is really awesome… because Daniel (the developer) has even created a client-server infrastructure, called Lagarto, that allows, among other things, sending data to Pachube, OpenSenSe, …