Recently I’ve discovered this project that has great ambitions:
arkOS is an open-source platform for securely self-hosting your online life.
Everything started from the founder Jacob Cook and the CitizenWeb Project he founded. It’s designed to run on a Raspberry Pi – a super-low-cost single board computer – and ultimately will let users, even of the non-technical variety, run from within their homes email, social networking, storage and other services that are increasingly getting shunted out into the cloud, and so under the control of big companies.
So in short arkOS is a lightweight Linux-based operating system that runs on a Raspberry Pi.