The stand-outs to me are the use of blue folder icons and the Dock.
https://www.retro-kit.co.uk/user/custom/Acorn/3rdParty/Retro...
What has been quite surprising over the years is how violently many people raised with Open/Save dialogs hate the Risc OS filer and approach to saving and loading files.
> He worked on the first generation of home computers and lead the design of the RiscOS operating system for the ARM processor, including inventing the apps and icon bar user interface that has since spread to phones and computers across the world
The RISC OS approach is like a million times better. The only thing I would add is a context menu to create a new file of whatever kind at this location, like The "New" menu in windows.
In my retrospective for the original Mac's 40th anniversary, I explained the technical limitations that forced this design:
https://www.theregister.com/on-prem/2024/01/29/the-real-sign...
A decade & a half ago, I put the original project team lead in touch with the London user group, which resulted in this talk:
https://www.rougol.jellybaby.net/meetings/2012/PaulFellows/
A decade later, I moderated a virtual interview with him and the surviving core team members:
https://www.theregister.com/software/2022/06/23/how-risc-os-...
One of the core team got head-hunted to NeXT in the USA. He took his Archimedes running RISC OS with him. Reportedly, he demonstrated it to his colleagues, and presto, the following beta of NeXTstep had this new "Dock" that was much like the Acorn RISC OS "icon bar".