Harvest - Simple time tracking, fast online invoicing, and powerful reporting software. Simplify employee timesheets and billing. Get started for free.

TimeLeft - TimeLeft is a versatile desktop utility - it can be used as a countdown clock, reminder, clock...

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.

Hourglass - Hourglass is the most advanced simple countdown timer for Windows.

Pomodone - Pomodone is the easiest way to track your workflow using Pomodoro technique, on top of your current task management service.

wnr - Better than pomodoro, this timer app balances work and rest.