Plan 9 was born in the same lab where Unix began. Old Unix hands will recognize the cultural heritage in this manual, where venerable Unix commands live on, described in the classic Unix style. Underneath, though, lies a new kind of system, organized around communication and naming rather than files and processes. - Preface to the Second (1995) Edition
Man pages for Plan 9 2nd edition. In Plan 9 installations man pages can be found in /sys/man/.