8½ (Plan 9)

8½ 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, 8½ has been completely rewritten into its successor rio in recent Plan 9 versions.