Hourglass - Hourglass is the most advanced simple 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.
SleepBot - SleepBot is a sleep tracking app available in Google Play and the Apple App Store.
SnapTimer - SnapTimer is a simple, free, portable countdown timer for Windows.
Talalarmo - Minimalistic android alarm