Mac software for developing a product video
You want ScreenFlow. The website isn't all that well designed, but ScreenFlow itself is a very nice and nice-looking Mac app. 

Depending on how fancy you want to get with transitions and effects, you might find it useful to export clips from ScreenFlow and composite them in something else. But there are plenty of product demo videos for popular Mac apps that  were done completely in ScreenFlow (examples elude me; help, commenters?).