I remember discovering the iOS calculator has a lot more features when you rotate the device into landscape orientation: http://osxdaily.com/2011/12/29/iphone-scientific-calculator/ I haven't tried recent iOS versions so I don't know if it's changed. According to the comments there, everyone and their dog knew this from birth, but I think it should count as "hidden" functionality, and rotating to landscape is kind of like right-clicking.