How about OSs that target the hypervisors? With hypervisors getting everywhere, it becomes a viable platform on which we can re-evaluate the assumptions we make about OSs.
For example, I'm working with a bunch of other people on MirageOS [1], which is clean-slate, library OS written entirely in OCaml and targets the Xen Hypervisor. Since Xen works on ARM devices, we'll also be able to create applications/appliances for the coming wave of embedded devices (aka Internet of Things) -- in addition to running things on the public cloud.
If you're interested in reading more, there's an ASPLOS paper [2] where you can find out more. There will also be a CACM article in the New Year that covers more of the wider background.
[1] http://openmirage.org and http://nymote.org/blog/2013/overview-of-mirage/