Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
NetTime - nettime is a time & attendance software solution.
SnapTimer - SnapTimer is a simple, free, portable countdown timer for Windows.
Dimension 4 - The fastest and easiest way to synchronize your Windows clock.
Free Countdown Timer - Free Countdown Timer is a free, full-featured and user-friendly countdown timer for Windows
Meinberg NTP - NTP client and server download for different operating systems.