@peter_haas @me_ @regehr oh, well, if you want my opinion....

Plan 9 had some really cool ideas, but they were products of their time, the place they were developed, the group that developed them, and the issues that were important to that group in that time and place.

The idea of per-process, mutable name spaces and small file trees containing end points for IPC as a means for building a system was interesting and led to some really elegant demonstrations: I've always liked how one could import one's namespace from a terminal onto a CPU server, thus being able to (privately!) access all of one's local devices remotely. No need for X11 or a network sound protocol; just open the relevant device file and you're done. In many ways, Plan 9 was a better Unix than Unix, which is unsurprising given who developed it.

But the question must be asked, is building a better Unix all that relevant? Are highly synchronous system interfaces and files as _the_ metaphor for system interaction still relevant in 2023? More importantly, should they be? I would argue that they are less so than in the late 1980s (and I think some good judges would agree with me on that).

Then there's the implementation.... Plan 9 worked well enough on the sorts of machines available at Bell Labs in the 80s and 90s, but let's be honest: these are interesting ideas ensconced in research-quality code. In terms of reliability, it seemed to exist in this limbo somewhat midway between 7th Edition Unix and 4.3BSD for, well, ever. And then there's the C dialect: I think this was a clear win in 1989. In 2023? Not so much. It underspecifies on important things (atomicity of primitive operations, for instance) and assumes too much (sizes of primitive types). Some things were pure misfeatures (members of unnamed structs embedded in a struct become elements of the outer struct and we can pun on those has led to some weird contention issues with locks and reference counts). These days, aesthetics of some constructs or typedefs aside, I honestly think that C23 does everything that Plan 9 C did, but better.

So yeah. Plan 9: a highly influential research system, and I actually do run it in a few places these days, but it never evolved to be the system I hoped it would become. There was more hope for commercialization of Inferno (as a reimplementation of the plan9 ideas) but of course that never happened either. More's the pity.

Interestingly, there's a tie-in to Plan 9 (and Inferno!) from Wirth's work: the `acme` text editor was based on ideas from Oberon.