Plan 9 from Bell Labs - manpages
 
manpages 1 Commands
manpages 2 System and library calls
manpages 3 Devices
manpages 4 File servers
manpages 5 Plan 9 File Protocol, 9P
manpages 6 File formats, misc
manpages 7 Databases
manpages 8 System administration
manpages 9 Introduction to kernel functions