This article is kinda garbage, it gets simple facts wrong in the first sentence of the abstract (and again in the second sentence of the article): Plan 9 is not

This article is kinda garbage, it gets simple facts wrong in the first sentence of the abstract (and again in the second sentence of the article): Plan 9 is not Unix. At all. It shares some ideas with it sure, but if that's enough to make something Unix so is Windows NT. It's also rather debatable that it "failed" - a lot of good research happened there and those ideas have gone on to influence production environments the world over.