If you're anything like me, you've never acquire the skill of knowing when your period is going to come. As young adulthood rolled around I came to the realization that I should probably figure out how to track my period. After, like, 10 minutes of Google searching I downloaded the app Clue. It is available for Android and iOs.
Basically you can track your period, ovulation, and PMS in this app. They offer different view in which you can look at past cycles or three months ahead, like in the calendar view below. You can even set a reminder or widget so you'll be notified days before your period begins.
They recently released an iOs update in which you can track your skin, weight, mental state, motivation, cravings, and weight. This way you can track what is related to your cycle and what is not.
There is information related to different birth control methods, and you can even set an alarm for your pill. Over all this app is sleek, easy to use, and it doesn't scream "period app" on your home screen. I use it pretty much religiously so I am always prepared!