Around 1977 or so, I worked with MOS, a "mini" operating system for the PDP-11. I think it was originally developed at SRI, to support the BBN Packet Radio networking research. It was written in assembly language, supplied in source form. Tasks were defined statically, at assembly time. There was a single-user TCP and Telnet. Someone else did a multplexer, to allow multiple tasks to set up TCP instances. It was a VERY simple thing, but it worked.
I've been trying to track down it down for a while, to no avail. It looks as though it has disappeared completely.
No, this isn't a "Fuzzball", although they appear to have similar purposes.
Does anyone have any pointers?