Around the same time I heard of Urbit, I was listening to Don Stewart talk on a podcast (Haskell Cast episode #2) about using Haskell to avoid running an entire OS in the cloud; only the necessary code to perform the necessary operations to integrate with other systems was necessary.

He was using Xen to run a GHC process which he describes as a "microkernel environment".

Xen + Language Runtime (ghc) + user functions = the whole stack, and this boots in milliseconds, using only 1 or 2 meg of memory.

What's interesting is that this is a technique that he's using in development today.

I didn't read all the Urbit documentation, but the concepts between Don Stewart's approach and Urbit seem to share some similarities with eliminating OS bloat.

Some folks have claimed Urbit is as much art at practical, but Don is already doing practical things like this; unless I'm mistaken about what Urbit is about (I'm sure it does a lot of other things differently as well).