Pinning a window to stay always on top can be handy when copying and pasting from one application to another.
The one that does the job is DeskPins which allows to pin the window by pressing Ctrl + F12. The pin icon is shown on the top right of the pinned window. Once the window is pinned then pressing Ctrl + F12 will unpin the Window.
The filesize of this software is just 586kb!