This is the first time I see Urbit, looks interesting. Do you have some context about the project? Project homepage (http://urbit.org/) doesn't seem to explain anything and Github page just describes the language.
You can search also for "Moldbug". He has an old blog.
He is also a very controversial guy with libertarian ideas.
His project is very neat with distributed processes called "ships" or "submarines" with rights based on reputation.
It's a little bit like Erlang processes but with an anti-spam security model.