Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
Horo - The best free timer app for Mac
wnr - Better than pomodoro, this timer app balances work and rest.
MultiTimer - The new application available on the App Store|Subscribe
Date Reminder - Date Reminder reminds you of recurring or nonrecurring events, like birthdays, bills to pay...
Chronograph.io - Cloud synchronized stopwatches and timers.