Go look at Genode, one of the most exciting things in OS development I've seen for a long time:

http://genode.org/documentation/general-overview/index

It's a secure microkernelly capability-based OS where each process is basically a virtualised hypervisor; it can run a conventional OS as a user process, but it's also got a Unix-like native personality if you want it. I believe it's nearly self-hosting.