Hourglass - Hourglass is the most advanced simple countdown timer for Windows.
Song Alarm - song-alarm - Simple alarm clock for Android that plays a selected song at a desired time.
wnr - Better than pomodoro, this timer app balances work and rest.
Talalarmo - Minimalistic android alarm
Date Reminder - Date Reminder reminds you of recurring or nonrecurring events, like birthdays, bills to pay...
Gentle Alarm - Gentle Alarm can consider your sleepcycles to wake you up when you are in light sleep.