Android: Popular sleep tracking app, Sleep Cycle, was previously only available on iOS. Today, Sleep Cycle has rolled out to Android users too, many of whom could benefit from a better night's sleep.
The app is designed to track your sleep movements (using your phone's accelerometer) and know when you're in the deep or light phase of sleep. It will then start to gently wake you up around your desired wake up time, based on your sleep cycles. So instead of being interrupted in the middle of your sleep cycle, causing you to be groggy and unhappy, the app intelligently wakes you up at the optimal time -- something regular alarm clocks can't do.
Sleep Time Alarm for Android is similar and free, but if you find that app (or others like it) haven't worked for you, the $2 investment in Sleep Cycle (the best rated sleep app for iOS) might be worth a try.