Taskful - Deadlines, meet your match.
Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
Calendarist - Time blocking companion for Google Calendar
wnr - Better than pomodoro, this timer app balances work and rest.
Centered - Centered helps you get into a Flow State faster and stay there longer so you can do your best work.
Free Countdown Timer - Free Countdown Timer is a free, full-featured and user-friendly countdown timer for Windows