Plan 9 From Bell Labs - UNIX Compatibility

UNIX Compatibility

Though Plan 9 was supposed to be a further development of UNIX concepts, compatibility with preexisting UNIX software was never the goal for the project. Still, many command line utilities of Plan 9 have aliases to the names of their UNIX counterparts.

Plan 9 can support POSIX applications and can emulate the Berkeley socket interface through the ANSI/POSIX Environment (APE). Some Linux binaries can be used with the help of a "linuxemu" (Linux emulator) application; however, it is still a work in progress.