Contrary to popular belief, Chaosnet is not extinct.
It’s actually growing in usage as emulation has lowered the cost barrier to entry and for operating the systems that traditionally used it. These are mostly Lisp Machines and PDP-10 systems running ITS and TOPS, but there are other implementations as well, such as Cisco IOS, VMS, MINITS-11, BSD UNIX, and Linux.
There are implementations of Chaosnet over Unix domain sockets, Chaosnet over UDP, Chaosnet over IP, as well as over Ethernet. Cisco IOS supports routing Chaosnet through at least IOS 12.2.
The small size and simpler implementation compared to other network stacks makes it well suited for resource constrained systems.
I am working on Chaosnet for BAN.AI Multics.
The main Chaosnet home on the Internet today would be the Chaosnet wiki.
Worth noting that DECnet also has public IP-encapsulated hobbyist networks online:
The software you probably want to use for getting started with all this minicomputer retrocomputing stuff is SIMH. It has a relatively easy to use tap ethernet driver that should let you get your machine online. I used OpenBSD VAX on simh a few years back and it was painless; more esoteric networking protocols will be more difficult. Use the new version of SIMH from github, the older versions are not worth your time.
I kinda want to see a SNA hobbyist network; VAXen get all the love!
BAN.AI Public Access Multics is actually on HECnet as node BANAI (1.770).
https://ban.ai/multics/doc/AIM-628_chaosnet.pdf is my copy of the “definitive Chaosnet reference”.