This Nixie Alarm Clock project gets the Time Updated via GPS. Not only is there GPS to get an accurate time, this clock also has an SD card that is used to play audio files.
“The firmware for the clock is written in C using Eclipse C/C++ with the AVR Eclipse plugin with avr-gcc and avr-libc 1.8.1
Since the GPS module provides the time in UTC, I need to handle time zone and DST in software. This is actually quite easy since the standard time.h functionality has been implemented in avr-libc 1.8.1. But as I started the development on Linux using 1.8.0 it took me a while to discover the newer avr-libc since there are still no official binary packages for avr-libc 1.8.1 even though it was released more than a year ago.”