Plan 9 From User Space is a port of the bulk of
the Plan 9 software build environment to Unix.
While the libraries make an attempt to play nice
with the rest of the system (by using the Unix
rules for printf verbs and Unix system headers,
for example), this port tries to reproduce the
Plan 9 build environment as faithfully as
possible, providing u.h and libc.h, and blithely
redefining tokens such as open, dup, and accept in
order to provide implementations that better mimic
the Plan 9 semantics. The result is a more
complicated and less Unix-friendly environment,
but Plan 9 programs can typically be compiled with
little or no changes.