The Jargon File (version 4.4.7, 29 Dec 2003):
In the late 1980s, researchers at Bell Labs (especially Rob Pike of
Kernighan & Pike fame) got bored with the limitations of UNIX and decided
to reimplement the entire system. The result was called Plan 9 in ?the Bell
Labs tradition of selecting names that make marketeers wince.? The
developers also wished to pay homage to the famous film, ?Plan 9 From Outer
Space?, considered by some to be the worst movie ever made. The source is
available for download under open-source terms. The developers and a small
fan base hang out at comp.os.plan9, where one can occasionally hear ?If you
want UNIX, you know where to find it?
The Free On-line Dictionary of Computing (18 March 2015):
(Named after the classically bad,
exceptionally low-budget SF film "Plan 9 from Outer Space") An
operating system developed at Bell Labs by many
researchers previously intimately involved with Unix.
Plan 9 is superficially Unix-like but features far finer
control over the name-space (on a per-process basis) and is
inherently distributed and scalable.
Plan 9 is divided according to service functions. CPU
servers concentrate computing power into large
multiprocessors; file servers provide repositories for
storage and terminals give each user of the system a dedicated
computer with bitmap screen and mouse on which to run a
window system. The sharing of computing and file storage
services provides a sense of community for a group of
programmers, amortises costs and centralises and hence
simplifies management and administration.
The pieces communicate by a single protocol, built above a
reliable data transport layer offered by an appropriate
network, that defines each service as a rooted tree of files.
Even for services not usually considered as files, the unified
design permits some simplification. Each process has a local
file name space that contains attachments to all services the
process is using and thereby to the files in those services.
One of the most important jobs of a terminal is to support its
user's customised view of the entire system as represented by
the services visible in the name space.