Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
wnr - Better than pomodoro, this timer app balances work and rest.
SnapTimer - SnapTimer is a simple, free, portable countdown timer for Windows.
Gestimer - For those little reminders during the day
Horo - The best free timer app for Mac
Date Reminder - Date Reminder reminds you of recurring or nonrecurring events, like birthdays, bills to pay...