Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
Toggl - Toggl is an online time tracking tool. It features 1-click time tracking and helps you see where your time goes. Free and paid versions are available.
Free Countdown Timer - Free Countdown Timer is a free, full-featured and user-friendly countdown timer for Windows
Hours - Boosting productivity through live, virtual co-working.
SnapTimer - SnapTimer is a simple, free, portable countdown timer for Windows.
Futuramo Time Tracker - Futuramo Time Tracker is a time tracking solutions designed for freelancers and teams.