Sleep Cycle - Bio-alarm clock that wakes you up at optimal times based on your sleep patterns.
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.
Talalarmo - Minimalistic android alarm
Pillow for iOS - An iOS companion that helps you sleep better 💤
AlarmDroid - AlarmDroid is an alarm application that is only available on Android devices and possesses many interesting features.
Gentle Alarm - Gentle Alarm can consider your sleepcycles to wake you up when you are in light sleep.