Somehow many Plan 9 fans seem to forget that the design continued as Inferno.

So with that in mind, I would rephrase that as "Inferno is basically a better Unix".

You can learn more about it, including the programming manual with lots of Limbo examples at:

http://doc.cat-v.org/inferno/4th_edition/

You can easily see some of Go's pedigree on Limbo's design.

Nowadays Inferno is still being sold by Vita Nuova, the company that acquired the rights after Bell Labs folded the project.

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