Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
Fitbod - Personalized Strength-Training powered by Machine Learning
Free Countdown Timer - Free Countdown Timer is a free, full-featured and user-friendly countdown timer for Windows
MyFitnessPal - Track the number of calories that you consume each day with MyFitnessPal. The app also lets you create a diet and track the exercise that you complete each day whether it's walking, running or some other type of program.
SnapTimer - SnapTimer is a simple, free, portable countdown timer for Windows.
Fitocracy - Fitocracy is a social network that turns exercise into a cooperative and competitive exercise with friends, rivals, and strangers.