> Plan 9 is an incomplete name. That company refers to themselves as
> PLAN9, which is not trademarked.

"Plan 9" is a registered trademark in the USA (reg 2065577, `operating system computer programs').
It is registered to Lucent Technologies Inc. That registration is in class 9, which is huge,
but the United States puts reasonably tight bounds on the scope of a trademark based on
the description of the Goods and Services within that class (unlike, say, the messed-up CTM system).
The apparent products of Plan9 Software is software consultancy, cheerful people who give you `thumbs up'
and a program called Qualify that is fully buzzword compliant with a suitably dire user interface
(to judge from the screen shots). The software isn't called Plan 9, nor is it an operating system,
and the set of cheerful people immediately prevents association with the registered trademark.