Zapper modifies the behaviour of the ZipWindow() function in intuition.
Instead of resizing the window to the alternate zoom values it will maximize the
window full-screen (avoiding the titlebar if there is one).
It is also capable of smart-resizing the window (making it bigger) over the currently
available empty desktop/screen space (where there are no other windows).

The image to the left shows the ambient screen with a few opened windows on it.
To the right is the result (with smart-resizing) after pressing the zoom button on
the leftmost and rightmost windows.