I propose “os” tag for “Operating systems”.
Here are some stories I think fit: Re-imagining Operating Systems: Xen, Unikernels, and the Library OS, OS Technologies To Watch. Curiously, both are tagged “devops”, which I think is inappropriate.
It seems like most OS stories that come up for discussion either have a tag for that OS (Linux, OpenBSD, etc) or are enough of a theoretical discussion that it fits under compsci. Both of those links seem fairly heavily Linux-focused (or are Linux-derived).
Both links discuss Mirage OS, which is completely unrelated to and not derived from Linux.