Using a technique called Reverse Electrovibration, REVEL (from Disney Research) uses a weak electrical current to simulate the sensation of tactile texture on any surface that has a common electrical earth with the human body.
On a touch screen device such as a phone or tablet, this technology could be used to greatly enhance onscreen virtual controls, such as a qwerty keyboard, or could even lead to hitherto unimagined types of applications.
Virtual musical instruments, for example, ​with haptic feedback could be very interesting indeed. Or how about a camera app with virtual textures that help the user to identify blown out highlights or crushed dark tones in a photograph or video?