I wrote Apple Shaped Windows back in 1985, to demonstate my sk!11z by writing a WDEF with an unusual shape. It also caused some excitement then. Now, 20 years later, here is a Windows version.
Apple Shaped Windows uses a Window Region to change the shape of the window. The apple shape is constructed from several oval regions. It is positioned in the client area of the window, and the leaf part is interpreted to be the window caption (the real caption is outside the region). A bit more region fiddling gives the window a sizing border.
The present application has nothing to show in the content area, but if there were real content to show, it would need to be clipped to the client region.
The leaf is the window caption. The green area is draggable. The red area is the close box. The white area is the Window (System) Menu. Clicking in the apple brings up the about box. Dragging the sizing border resizes the window.