rio is the latest in a long series of graphical user interfaces developed at Bell Labs, mostly developed by Rob Pike, the concurrent window system, and the Blit (which predated X).

According to its documentation, the system has little graphical fanciness, a fixed user interface, and depends on a three-button mouse.

Because of the limitations stemming from its unusual implementation, 8+1⁄2 has been completely rewritten into its successor rio in recent Plan 9 versions.

Its main change was that it stopped parsing and rewriting graphical commands and let the client write pixels directly.

As Alef disappeared due to being too difficult to maintain given the number of people working on Plan 9 at the time, rio was rewritten in C. This was done using the Plan 9 thread library which was inspired by Alef and had most of its features, such as blocking channels for interthread and interprocess communication.