I've looked through its documentation, and while I couldn't make heads or tails of it, Urbit seems to be everything but an operating system. Espeically that it needs unix system to run.
Urbit is an OS in that it defines the complete lifecycle of a general-purpose computer. It's not an OS in that it's the lowest layer above bare metal.
Sorry you had a bad experience with the docs. Urbit is actually much stupider than it looks.
Unfortunately, premature documentation is the second root of all evil, so some of the vagueness you sense is due to immature code. It's always a mistake to document a system into existence -- that is the path of vaporware. Better to run and have weak docs, than have good docs but not run.
I'm not criticizing, I am exposing that I am part of the problem and lost, and I'd like to know how people handle this on their lives. I want to document more but there's always this rush to implement implement implement and not once, during some catastrophic breakdown of something, management wants everything solved quickly but they expect you to remember instantly of everything you did 2+ years ago :-)
PS: ... and they'll get mad if you say "you didn't let me document this damn thing"