The Byte article (the scan of which I am very grateful for; not having to go trawling through the stacks at the Oberlin College library is always a plus) claims that the tools have been implemented on:
Tandem
That would be me; at least I registered it with Addison-Wesley, although someone else may have implemented it independently. I also wrote a shell that took advantage of Guardian-style IPC, using a per-user pipe server that connected up all the monodirectional pipes through itself. Its prompt was ::, which the documentation referred to as the quadpoint prompt.