If you want to build a digital clock with unique features then check out DOTKLOK project. This Arduino-based digital clock can displays a series of unique time-telling animations. The passing of time is displayed with numbers and abstract/geometric patterns taken from classic video games such as Pong, Tetris, Pacman, and Space Invaders. The clock is totally hackable. Its circuit board has prototype area and all unused Arduino pins are available so user can add more switches, buzzers, sensors, etc.
The main part of the clock is AVR ATmega328 MCU running the Arduino bootloader and DS1307, a real-time clock (RTC) chip with back-up battery to keep time and date accurate even when the power is absence. Here are the clock features including, 12 user-selectable time animations, 24/12 hour modes, “random mode” can switch animations each day at midnight, 4 button time/display interface + slide switch for mode selection, UL + CE universal power supply included. This animation digital clock project is created by Andrew O’Malley and is released under open-source license.