Proposal: Operating Systems
This site has nothing to do with SU, but it does have trouble differentiating itself from SO. There are precedents for sites carving out a topic with significant overlap with SO, such as Database Administrators and Game Development. But the OS development proposals (this isn't the first one) seem to be subsets.
My day job is to develop embedded software including an operating system. I find the Embedded systems proposal relevant, because it covers a lot of topics that SO doesn't, but I'm struggling to find a use for a separate site about OS development.