For me personally, IRIX 6.x had one of the most beautiful (and colourful) GUIs ever.
For the curious, there is a guide (1) on how to run IRIX 6.5.22 in MAME.
Someone did a screen capture of a SGI "System Tour" app that explains how a lot of the UI worked:
For those interested, there is a lovely IRIX clone WM called MaXX. I've been using it for a couple months and have been quite happy with it on a remote dev machine. I believe it only runs on xorg currently.
What is the scrollwheel thing on the left side of some windows?
Wow, look at those luxurious titlebars, windows edges, scrollbars, and tabs! So easy to use.
One other thing lost, their scrollbars kept an indentation of where the bar was until you let go, which was sometimes useful.
Not a fan of the busy backgrounds, but can’t win ’em all.
Does anyone have a screenshot of the window menu (right click on titlebar)? Been looking for the CUA hotkeys related to those window functions. Most still work but are not shown on Linux desktops for some reason.