[pjc50]

> Even totally plain-looking device could be full of innovative research: a network router which uses completely new kernel.

True. Although all those kinds of devices tend to prefer "free" over "innovative", and to keep the OS layer as thin as possible.

> A new network protocol or a compression algorithm. New programming language. Automatic verification and/or fuzzing tools.

To me those aren't really systems software, but that may be a matter of opinion?