Using e-paper in electronics projects significantly reduces power consumption. This is because display uses power only on screen updates and draws zero current on static state. Kevin has been working on e-paper based clock project. E-paper display he uses comes with film connector. Luckily SparkFun has a breakout board for them. Without hesitation he grabbed one and made a mother board for it. Clock is driven by Atmega328P microcontroller. It takes care of refreshing display and reading time data from Ds3231 RTC chip.
In order to make this clock portable he included a 1000mAh Lithium Ion battery. Battery can be charged using MCP73831 charge IC and USB power. Kevin put some effort to make design pretty unique including small details like motherboard cut-offs and acrylic stand. Functionality seems all set, the only thing is left to work on code efficiency, because it seems that battery drains over few days. Less screen refresh and sleep modes should fix this.