Answering the second question: you won't want to use it in production, but if you have ever been intrigued by one of those Unix philosophy preaches, you should definitely take a look at it. It takes the tool philosophy (build simple tools that are easy to combine) and filesystem metaphor much further, besides addressing some (albeit not all) long-standing Unix WTFs.

Plan 9 is not the most elegant design of OSes, but its simple ways of combing primitives are pretty amazing. Simplicity is underappreciated nowadays.

plan 9 is the earlier effort of re-engineering Unix and runs on hardware. It was meant to replace Unix, but it never did.

With inferno they went the VM route (the dis VM) and built it so that it runs on myriad platforms, from Unix and ActiveX. It still runs on hardware though. The intension was that you can run a network of hosted and native inferno installations, making it easier to adopt. Unfortunately, inferno saw no widespread adoption either.

The underlying filesystem concept is basically the same (the latest version of 9p and Styx are identical), but the programming environment changed a lot (you write limbo to run on dis). Also the user space programs were rewritten and get overhauled a bit. The community never get divergent enough though; inferno people tend to identify themselves as part of the plan 9 community.

Are you very specifically interested in running an ARM port targeted at the Raspberry Pi? If you just want to try Inferno or Plan 9 generally, try:

http://www.vitanuova.com/inferno/downloads.html

http://plan9.bell-labs.com/plan9/download.html

VirtualBox is for x86 CPUs only. It doesn't support ARM. You need something like qemu instead.

Why would you have a Pi instead of a MacBook Pro?

Rhetorical question is rhetorical.