SleepBot - SleepBot is a sleep tracking app available in Google Play and the Apple App Store.
Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
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.
SnapTimer - SnapTimer is a simple, free, portable countdown timer for Windows.
Sleep Cycle - Bio-alarm clock that wakes you up at optimal times based on your sleep patterns.
wnr - Better than pomodoro, this timer app balances work and rest.