What are some alternatives?
When comparing Gentle Wakeup and Sleep as Android, you can also consider the following products
Free Alarm Clock - Free Alarm Clock is a free, full-featured and user-friendly computer alarm clock for Windows.
SleepBot - SleepBot is a sleep tracking app available in Google Play and the Apple App Store.
Sleep Time - Alarm Clock - Sleep Time provides insight into your sleep patterns. By tracking your level of movement throughout the night, Sleep Time generates customized sleep data in easy-to-read charts.
Talalarmo - Minimalistic android alarm
Alarmy - World's most annoying alarm app
Gentle Alarm - Gentle Alarm can consider your sleepcycles to wake you up when you are in light sleep.