An awesome (even if not open source) solutions is debuting on the market: Dweet is like Twitter for Things!
Ridiculously simple messaging for the Internet of Things.
Fast, free and ridiculously simple— it’s like Twitter for social machines.
If your product, device, machine, gadget or thing can connect to the Internet, it can use dweet.io to easily publish and subscribe to data.
dweet.io doesn’t require any setup or sign-up— just publish and go. It’s machine-to-machine (M2M) for the Internet Of Things (IOT) the way it was meant to be.
dweet.io – Share your thing- like it ain’t no thang..
Check out how to use Dweet with raspberry pi : http://www.element14.com/community/community/design-challenges/forget-me-not/blog/2014/08/29/fmn05-why-tweet-when-you-can-dweet