I'm old enough to remember a bunch of demos using window position/dimensions from back in the day. I remember one with a physics simulation. I can't remember if it was liquid or just a bunch of solids, but you could drop things from one window to the other.

IIRC you don't even need the sockets. One can simply use message channels between the windows. If a window opens child window, iirc it has special access over it (I say special, because usually different tabs/windows are isolated from one another) which might make a local-only version easy to implement too.