I'm working on a project with one of the points in mind. Its an API that allows popular embedded cards (arduino, raspberry pi) to message each other through the web. It called bbedy (<a href="https://github.com/bliti/bbedy" rel="nofollow">https://github.com/bliti/bbedy</a>). This is version 0.2, and it is mostly functional.<p>The aim of the project is to enable the exchange of (sensor) data between devices. It is driven by a simple protocol I'm about to publish on github. The idea came to be when I did not have any way of exchanging data between two raspberry pi projects I was working on. I prototyped a very crude version and it worked very well. I decided to create an open source version that could be easily pushed to Heroku or any Django-enabled web host (like webfaction).
ETA for the project is January 2014. Shoot me an email if you'd like to know more.