Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
SleepBot - SleepBot is a sleep tracking app available in Google Play and the Apple App Store.
wnr - Better than pomodoro, this timer app balances work and rest.
Sleep as Android - Common alarm clocks ignore your sleep cycles, they wake you on schedule no matter your are currently in your deep sleep. Waking up from deep sleep is unpleasant, it makes you tired and it may negatively affect your productivity during the whole day.
Date Reminder - Date Reminder reminds you of recurring or nonrecurring events, like birthdays, bills to pay...
Sleep Cycle - Bio-alarm clock that wakes you up at optimal times based on your sleep patterns.