(This was also the OS with the first icon-based taskbar, before NeXTstep and its Dock; and also the first GUI where dragging a window to move it moved the window contents, not just a dotted outline. It's the original inspiration for the Windows 95 taskbar.)
https://en.wikipedia.org/wiki/RISC_OS
(This was also the OS with the first icon-based taskbar, before NeXTstep and its Dock; and also the first GUI where dragging a window to move it moved the window contents, not just a dotted outline. It's the original inspiration for the Windows 95 taskbar.)
There are a couple of pics of v2 here:
https://www.houseofmabel.com/personal/computers/riscos/
And a gallery of RISC OS 3:
http://toastytech.com/guis/riscos.html