And Mach is a Unix kernel. Therefore it is Unix.
Linux isn't Unix. From an end user perspective it doesn't really matter since it walks and talks like that duck, and "Unix", from an end user perspective is more about the BSD tools than much of anything anyway, since you can run any shell on almost anything and the nittier and grittier stuff is only really relevant to IT professionals whose job is to make it work as close to advertised as is humanly possible, and religious software engineers, but NeXT and its flavors called OpenStep and OSX are not NT and it's not even arguable that they're the most successful modern implementation of Unix there is, not only for doing what the Linux crowd still cannot but also for what came to life on NeXT and the NeXT technology that powered a fledgling internet as it gained mainstream and enterprise acceptance.
And trust me, plain 4DWM looks terrible by comparison. I scaled down the widgets,and cleaned up the general configuration. If you don't have experience with the 6.5.22 or above its totally different from the 4 and 5 and even the early 6 series.
But your screenshot only shows an improvement in the right, left and bottom frame borders, making them almost disappear compared to default. The top bar is still generic and unattractive with non-antialiased text. Or do you just not have a picture of this "totally different" 4DWM? Because that's effectively just a slightly anorexic looking version of bland as it ever was 4DWM and icons that go all the way back to pre-4DWM IRIX (which, icons didn't matter then or later since the "desktop" functionality of IRIX was pretty much ignored in the context of how alternatively useful this mode of machine interation is on Mac and Windows). Roll back to the SS I posted just grabbing a 4DWM picture from the net and your's is not appreciably any more attractive, it's just put window borders on a diet.
I looked at the dates and the last version of IRIX I used was earlier 6.5.xx (up to about 6.5.12 or so), because by 1999 they had failed to keep up with Intel and now they were far too expensive for how slow they were. Here we had multi-proc, multi-core Xeon systems becoming affordable and your average SGI workstation at the time was still P3 class performance with a small mortgage or car payment attached.
As much as I was not a fan of NT the absolutely stupidly designed, Xeon-powered 540 was a shot in the arm for productivity for a couple years in 1999 before BoXX and HP and even Dell systems running various grungy flavors of Linux with shoddy gfx drivers took saved us from a Windows future. In 2000 I ended up working freelance at this little boutique and was saddled with an Octane and it was just awful going so backwards, even though it was as upgraded as one could. Except for vector and shading performance the shiny new PowerMac I bought that year felt faster.
Guys drilling for oil, universities, etc. likely still used SGI after 1999 but only facilities locked into server class hardware for Flame and Inferno (or just still paying off workstations nobody wanted anymore) continued to burn money on SGI after the Turn of the Century.
4DWM, by then, could have had hot and cold running Jolt Cola and it wouldn't have mattered because the hardware was so not up to iterative compute intensive tasks any longer and there in the early days of OSX and the beginning of the buzzword for "cluster" computing they didn't have much leg to stand on in massively scalable computing either. And at the end of the day, nothing that's ever been done to 4DWM makes it more attractive than IRIX 3.3 and I call your bluff on them really changing much of anything at all...here:
IRIX 4.0.1
IRIX 5.3
IRIX 6.5
...third verse, same as the first.
