OLED or Organic Light Emitting Diodes almost have endless use in almost every domain in electronics. Check out this simple clock from Designer Vadim Kibardin. As you can see the clock is rather unique in design, it does not have any case. All you need to do is just put four of the the individual digits, that would complete the clock.
The digits are in sync and a “light sensor switches the numerals from black to white, displaying the correct time, day or night.” The device is still in a conceptual stage and the designer is looking for a manufacturer.