Arduino_segment_watch is a project mainly written in C++ and C, it's free.
from scratch source for the Sparkfun "BigTime" watch from Maker Faire
This is an on-going firmware replacement for the big time watch sold at Maker Faire NY 2011.
The goal is to add functionality for timers, alarms, stop watches, and a trip count-down (based on an input MPH)
Current code works to update the time every second and go in to a deep sleep otherwise.