I remember trying out Plan 9 a few years ago. I like its underpinnings; I like how the designers pushed the Unix notion of "everything is a file" to its limits, with various services being presented to the operating system as file servers implemented using a protocol named 9P. It's a cool research operating system with a lot of very interesting ideas, but ultimately it's not my daily driver due to a lack of hardware and software support, though I am working on a research project (but for conventional *nix operating systems) that takes advantage of 9P.
Carmack's description of the rio GUI is apt; rio is heavily based on Xerox PARC's Cedar environment from the mid-1980s (https://www.youtube.com/watch?v=z_dt7NG38V4). I had a hard time getting used to rio, though eventually I learned it. I even purchased an old Sun three-button mouse (with no click-wheel) since Plan 9 didn't like my click-wheel mouse. rio does not adopt a lot of the conventions that were introduced by the Apple Lisa, Apple Macintosh, and Microsoft Windows, resulting in a completely foreign experience for most new Plan 9 users. There is a misconception that Apple and Microsoft simply stole the idea of GUIs from Xerox PARC without further innovating on it. This misconception is false; the Apple Lisa and the Apple Macintosh introduced many GUI conventions that were not present in Xerox PARC's GUIs (this video comparing the Apple Lisa to the Xerox Star highlights the differences: https://www.youtube.com/watch?v=pBiWtJJN5zk), and Windows introduced additional innovations. Back to Plan 9, the result is a GUI that has many conventions that were explored by Xerox PARC but were not adopted by the Mac or Windows, such as mouse chording (https://en.wikipedia.org/wiki/Mouse_chording). Hence, there's a learning curve for those accustomed to conventional GUIs.
Even so, the ideas behind rio seem to do a good job with exploiting Plan 9's architecture and showing how it could support a more tools-oriented design. Moreover, it was borrowed from Xerox PARC's Cedar. It would have been quite a research effort to create a Mac- or Windows-like GUI for Plan 9 that made full advantage of Plan 9's "everything is a file" architecture. Merely implementing a Mac- or Windows-like GUI to Plan 9 might not have taken full advantage of Plan 9's architecture, which I think is the key difference between Plan 9 versus other operating systems.
Perhaps in some alternate universe where Apple and AT&T merged in the 1990s and Apple built their successor to the classic Mac OS on top of Plan 9 with Apple people like Larry Tesler, Bruce Tognazzini, and Alan Kay joining forces with Dennis Ritchie, Ken Thompson, and Rob Pike....come to think of it, it's quite interesting to think about that possibility, though I don't think Apple would have made its post-1997 comeback without Steve Jobs, no matter how good "Mac OS Plan 9" would've been.
Carmack's description of the rio GUI is apt; rio is heavily based on Xerox PARC's Cedar environment from the mid-1980s (https://www.youtube.com/watch?v=z_dt7NG38V4). I had a hard time getting used to rio, though eventually I learned it. I even purchased an old Sun three-button mouse (with no click-wheel) since Plan 9 didn't like my click-wheel mouse. rio does not adopt a lot of the conventions that were introduced by the Apple Lisa, Apple Macintosh, and Microsoft Windows, resulting in a completely foreign experience for most new Plan 9 users. There is a misconception that Apple and Microsoft simply stole the idea of GUIs from Xerox PARC without further innovating on it. This misconception is false; the Apple Lisa and the Apple Macintosh introduced many GUI conventions that were not present in Xerox PARC's GUIs (this video comparing the Apple Lisa to the Xerox Star highlights the differences: https://www.youtube.com/watch?v=pBiWtJJN5zk), and Windows introduced additional innovations. Back to Plan 9, the result is a GUI that has many conventions that were explored by Xerox PARC but were not adopted by the Mac or Windows, such as mouse chording (https://en.wikipedia.org/wiki/Mouse_chording). Hence, there's a learning curve for those accustomed to conventional GUIs.
Even so, the ideas behind rio seem to do a good job with exploiting Plan 9's architecture and showing how it could support a more tools-oriented design. Moreover, it was borrowed from Xerox PARC's Cedar. It would have been quite a research effort to create a Mac- or Windows-like GUI for Plan 9 that made full advantage of Plan 9's "everything is a file" architecture. Merely implementing a Mac- or Windows-like GUI to Plan 9 might not have taken full advantage of Plan 9's architecture, which I think is the key difference between Plan 9 versus other operating systems.
Perhaps in some alternate universe where Apple and AT&T merged in the 1990s and Apple built their successor to the classic Mac OS on top of Plan 9 with Apple people like Larry Tesler, Bruce Tognazzini, and Alan Kay joining forces with Dennis Ritchie, Ken Thompson, and Rob Pike....come to think of it, it's quite interesting to think about that possibility, though I don't think Apple would have made its post-1997 comeback without Steve Jobs, no matter how good "Mac OS Plan 9" would've been.