I notice that on the Blit, new windows are created by "sweeping", i.e., dragging with the mouse from one corner of where the new window will go to the opposite corner. To this day, that is how new windows are created on the Plan 9 operating system.

(Specifically, you indicate using a command on a menu that you wish to create a new window. Instead of a new window appearing, like it would on any other OS, the cursor changes shape. The shape change is your cue that you can now "sweep", and the new window is created where you sweep, i.e., in such a location and with such dimensions that your sweep is a diagonal of the new window.)

And here is an opportunity to point out my pet hypothesis as to why no one uses Plan 9: namely, the refusal by the leaders of the Plan 9 project to adapt to what later became standard ways of doing things.

Although the Blit preceded the Mac, the Mac became orders of magnitude more widely used. And when Microsoft created an operating system with a GUI, they made opening a new window work like it does on the Mac. Once hundreds of millions of computer users had become used to the way one makes a new window on a Mac, Plan 9 should have changed to the Mac way. This is just basic hospitality. If you run a hotel and the controls for the hot and cold water work differently than the way they work in 99% of the homes of your guests, you hire plumbers to change the controls to work the way your guests expect them to work.

For some reason, the Plan 9 folks, and Rob Pike in particular, never saw the need for being hospitable (maybe because the way his software let the user create windows was invented first, damn it!)

Emacs has a bit of the same problem (inhospitableness, e.g., having unusual names for things, e.g., calling windows frames and calling panes windows), but Plan 9 is the most inhospitable software I've ever encountered.

Deleting text by highlighting an extent of text (e.g., by dragging the mouse), then hitting backspace is another example where Plan 9 behaves differently than every other OS I know about. (Particularly, it causes the highlighted extent to be deleted, like other OSes do, but then also deletes one additional character, which is unusual behavior that a user has to learn -- and then unlearn every time he or she switches back to a "hospitable" OS.)

In contrast, the designers of Gnome and KDE, for all their faults (e.g., being too eager to re-invent things) understood and practiced basic hospitality towards the user.