If you want to learn how you slept, the Sleep Cycle app is for you. It tracks your sleep patterns and provides tips to optimize your snooze time. Plus, it has a an alarm clock that gently wakes you up when you're in your lightest sleep phase so you'll wake up feeling refreshed. Just keep in mind that no sleep tracker is 100 percent accurate so if you're really struggling with your sleep, you may need to see a dedicated sleep specialist.
Cost: free