Nothing to see here yet. (OK, OK, I'll give you these:)
Some sources indicate that the Network Station 300 operating system (and perhaps the Boot Monitor firmware, too) is actually not developed by IBM, but by a 3rd party company called Network Computer, Inc (now Liberate Technologies.)
It also appears that the operating system is a proprietary derivation of NetBSD, and it has been claimed that the actual in-house name for it is NCOS (short for Network Computer Operating System), which would, of course, be fitting for an OS supposedly developed by a company called Network Computer, Inc.
I have not yet had the time to do any check-ups on these claims but they do seem plausible. I would gladly accept any further information on the subject.