I use Plan 9 extensively and intensively, and I believe there are multiple reasons why it is comparatively little-known and little-used. I think the most import

I use Plan 9 extensively and intensively, and I believe there are multiple reasons why it is comparatively little-known and little-used. I think the most important reason is the historical conflict over software patents between Rob Pike and Richard Stallman, and the cultural rift that it represented. Plan 9 is now under a pretty decent permissive license, but it still doesn't really function in the manner of a conventional open source operating system project. By the time Plan 9 was under a decent license, the mindshare of FOSS developers and the corporate ecosystem were already completely committed to other projects. Plan 9 is still relevant and interesting and useful for some tasks. It may still be ahead of its time. Plan 9 has had data deduplication for about a decade, years before network data dedupe storage appliances became an important product. The Linux kernel is still struggling to figure out a decent way to implement union directories in filesystems, but unions have been working elegantly in Plan 9 since its early days.