8½ (Plan 9)
is a window system developed for the Plan 9 from Bell Labs operating system by Rob Pike. According to its documentation, the system has little graphical fanciness, a fixed user interface, and depends on a three-button mouse. Like much of the Plan 9 operating system, many operations work by reading and writing to special files.
Because of the limitations stemming from its unusual implementation, has been completely rewritten into its successor rio in recent Plan 9 versions.
