How do you keep a window in all spaces? Some apps have this as an internal feature, but is there any way to keep a specific window visible no matter which space you're in?
I figured out how to keep an entire application on any screen.


Right click the application in the dock
Mouse-ver Options
Select All Desktops from the Assign to sub-menu.


But what if I just want, say one spreadsheet in excel to follow me to any desktop, while it keeps the rest where they are?