xPL.Arduino is an implementation of the xPL Protocol for Arduino. Old repository can be found at https://code.google.com/p/xpl-arduino/

It works independently of the ethernet shield.

There are four examples with the library, two for the official wiznet ethershield (send and receive) and two for the enc28j60 based ethershield.

Test on Arduino Mega with enc28j60 ethershield and the ethercard library : https://github.com/jcw/ethercard

Features:

No link with hardware
Auto send heartbeat messages
Parse received xPL messages and send result to a callback define by you
Send xPL message 

You can find some help here (in french) : http://connectingstuff.net/blog/xpl-arduino/