datagubbe

May I recommend to RISC OS users a couple of articles about graphical user-interfaces:

https://www.datagubbe.se/decusab/

and (RISC OS gets a mention in this sequel)
https://www.datagubbe.se/usab2/

It is clear that Carl Svensson came to computing through the Amiga rather than the Archimedes, but I am sure that his website https://www.datagubbe.se/ will be a rich source of interest to many on this forum.

With the exception of Plan 9 and RiscOS, all of those systems, and a majority of the applications running on them, were instantly recognizable and usable for me

Probably got stuck with the missing menu bar.
Context sensitive menus, fully described in the Welcome guide, were a genius idea because in the old days (think MODE 12) it would have been unacceptable to waste such large chunks of the screen on something that doesn’t get used enough to justify having it always visible.
Sure, these days you can say it isn’t an issue with screens that are like 4000×2000 or so, but back when it was more like 640×480 (or, worse, MODE 12), the space taken mattered. Moreso with Windows where the menu was wasted space at the top of each window.

However, if you’re used to the on-screen menus, RISC OS will be alien.

Likewise if you’re used to the tedium of opening a file widget, navigating to the correct folder, then telling the software to save your file there, RISC OS will be alien.

I think, to be honest, that a lot of these design decisions were compromises. Ask yourself why menus need to be always there. Ask yourself why RISC OS offered proper drag and drop while it’s contemporaries came up with better clipboards to work around the fact that the system just didn’t allow saving a file from one app directly into another.

Plan 9 is difficult to use.

It was through Thom Holwerda’s article Why I use KDE in OSnews that I found the link to Carl Svensson’s pages. I suspect that his journey, far deeper than mine, into Computer Science, full of resonances with my own. For many years I used RISC OS for everything. As RISC OS fell behind I started to use Linux, and kept finding difficulties because because my thinking was still GUI- not commandline-based. I had seen enough of Windows to avoid that. Now I hardly use RISC OS at all, despite it having the best GUI. I used to complain about the dearth of discussion about GUI design. Now I too use KDE, both in RaspberryPiOS and Manjaro on the Pinebook Pro. Its configurability is excellent, but its graphical metaphor is not as consistent as RISC OS.

Probably got stuck with the missing menu bar.

I had the misfortune of being tagged as the guy that knew GUI systems, so when there was a problem with the A&E consultant’s Mac…
I hated the f’n menu bar with a passion, I’m sure I was developing RSI in my arm joints just from zipping up to it and then back down to the work area every five seconds, and that one button mouse deserved burial in the deepest mine flooded with toxins.

Er, sorry, where was I? Ah yes, I don’t think the menu bar was a good idea at all.

With me I’d used the BBC Micro and UNIX (and often using the BBC Micro to access UNIX at university), then initially the command line on Arthur all before the RISC OS GUI, so after a regrettable dalliance with Windows for previous jobs, Linux and it’s command line is like coming home.

that one button mouse deserved burial in the deepest mine flooded with toxins

I suspect one of the guys at work likes them. Why? Because he’s written some documentation for a Windows-based system and keeps saying “select the [item], then click on the three dots¹, then select Edit” instead of “right-click the [item] and click Edit”.

¹ I know the article went into this, but it’s like someone combined a menu bar with a context menu, except in a random part of the screen and (usually) devoid of context!