OK, here’s a trick that works with Windows 7.
If you have several Windows open on your desktop, give this a try. Take your mouse and left-click and hold on the title bar (top) of one of the Windows, as if you were going to drag it. Instead of just dragging it, shake it back and forth vigorously. All the other Windows will minimize. Shake it again, and they will restore.
Update: This trick finally stopped working on Windows 11.