Plan 9 continues to grow and adapt. The fourth major release of the system incorporates a number of changes, but the most central is the conversion to a new version of the 9P file system protocol. - Preface to the Fourth (2002) Edition
Plan 9 current editions man pages. In Plan 9 installations man pages can be found in /sys/man/. Pdf version is also available.
1 - Commands 2 - System and library calls 3 - Devices 4 - File servers 5 - Plan 9 File Protocol, 9P 6 - File formats, misc 7 - Databases 8 - System administration