I have used inferno every work day for the past several years, either as Acme-SAC on Windows or natively compiled on a Linux machine. I have found that the minimal unix, coupled with the Acme interface, mean I spend a lot more time getting things done, and a lot less time (almost zero) retyping. Since it's a VM with its own shell and systems language, I can port my daily tools easily between whatever machines I'm working on, which has been great at client sites where I can just run my environment from a usb stick on one of their loaner computers.
I am very excited to see real usage of ~obscure OSes.
Other articles on this blog mention even lesser known ones.
What is Inferno?
An alternative distributed os, descendant to plan9.
I'm with you. I find it odd that after a rather long blog post about it, I still had no idea what it is.
Previous entries on the blog cover introductions to the OS in a bit more depth. Introductions for it are not too difficult to find overall, but anything past scratching the surface is less easy to find; that's the gap I was attempting to fill.