The Fuzzball PDP-11 operating systems by David Mills et at.
See https://www.eecis.udel.edu/~mills/gallery/gallery10.html
The Fuzzball is an operating system and a package of applications for the Digital Equipment Corporation (DEC) PDP11 family of computers, including the LSI-11 board-level components. The package was conceived in 1971 as a replacement for the RAMP operating system for the DEC PDP8. It later was evolved as a virtual machine supporting the DEC RT-11 operating system and early developmental versions of the TCP/IP protocol and applications suite. Prototype versions of popular Internet tools, including Telnet, FTP, DNS, EGP and SMTP were first implemented and tested on the Fuzzball. Fuzzball is now in the Computing Dictionary and remembered in the NSF history archives.
Fuzzballs were deployed extensively in the DARPA SATNET program during the 1970s. Fuzzball nests were deployed at the INTELSAT earth stations in the US, UK, Germany, Norway and Italy. Perhaps the best known role of the Fuzzball was as routers for the NSFNET Phase-I Backbone Network, which was deployed during the 1986-1988 time period. There were five routers co-located at the five NSF supercomputer centers and connected by 56-kbps data circuits. The Fuzzballs carried traffic between the centers, the center users and the adjacent college campuses.