Plan 9 from Bell Labs is a distributed operating system which originated
from the Computing Science Research Center (CSRC) at Bell Labs in the
mid-1980s and built on UNIX concepts first developed there in the late 1960s.
Since 2000, Plan 9 has been free and open-source. The final official release
was in early 2015.
Under Plan 9, UNIX's everything is a file metaphor is extended via a
pervasive network-centric filesystem, and the cursor-addressed, terminal-based
I/O at the heart of UNIX-like operating systems is replaced by a windowing
system and graphical user interface without cursor addressing, although rc,
the Plan 9 shell, is text-based.