While not the most common app, it's not surprising that there are several apps like this available (both free and paid). The first one I've come across that I use regularly is Period Tracker Lite (available for iPhone, iPod touch, and iPad).
The first screen allows you to view how many days are left before your period starts or how late your period is. You can also easily tap to say that you've started your period. It will track the days until you tap again to indicate that your period has ended. Here, you will also see flowers on the days you are ovulating. The app also predicts your future periods. You just enter how long your periods usually are and it will predict when (based on previous period) your next period will be.
It allows you to easily put in your mood, make notes of symptoms, track regular symptoms and how intense they are (light, medium, heavy). It also allows you to mark days of intimacy and shows you when you are likely to ovulate within the month. You can change the setting so that you have to enter a 4-digit passcode in order to open the application (in case your phone ever gets handed around).
The app also has a great feature where you can e-mail the data you have collected to yourself or anyone (i.e. your doctor) in case you need it for any reason. No longer will you have to make marks on your calendar or try to remember what day your periods started and ended when you head into the doctor.
If your doctor changes your birth control or changes your dose, you can easily make a note on the date it changed and list when you've stopped or started taking the medication and see how that might correspond to its affects on your body.
A simple app for savvy, busy women. I would download this today and start tracking now.
