In case you don’t know, “iconify” was a pretty common feature in older UNIX window managers (and still has some support in modern minimalist window managers/desktop environments like FVWM3, XFCE, EMWM, etc.) whereby when you minimize a window a small icon for it appears on the desktop in a tiny square box that you can later click on to restore. Sometimes, like in IRIX, the icon in the iconified box would be different than the normal icon for that app.
As you minimized icons they would form a row of boxes on the edge of the screen (you could control where the row went and move the boxes around willy-nilly).
Solaris example (Netscape and text editor in upper left)
I think NextStep also had it. I’m surprised KDE didn’t retain it when it began all those years ago as a free CDE-like. It seems that GNOME and KDE were both trying to merge the CDE “dock+virtual desktops” features with the Mac/Windows convention that desktop icons were passive representations of things that hadn’t been opened yet, and that icons for currently-running programs went in a taskbar.
But I think that’s a shame because the iconification approach is generally less cluttered and more flexible (you can move them around willy-nilly, while taskbars have to be moved all as one big thing and you can’t just put them anywhere only on screen edges).