Electric Sleep:
https://play.google.com/store/apps/d...leepbeta&hl=en
It's a sleep cycle alarm clock. Set the alarm, place the phone on your bed and it'll use the accelerometer to detect when you are in a light sleep phase right before your alarm time and wake you up then when your easy to wake up. It also is useful afterwards to track exactly when you fell asleep and how long you were actually asleep for.
There's also another one that's more updated called Sleepbot but when I tried it, they couldn't let you change the wake up alarm tone which was a deal breaker for me.