The 'Freya' app gives women a comprehensive menstruation calendar that they can use to track their periods.
The app features a wheel -- similar to those that hold birth control pills -- that show the dates of each month. Along that wheel are differently colored spokes that represent different pieces of information while showing how the user's body is acting at specific times of the month. The red spokes represent menstruation, orange represents fertility and blue represents infertility. This is an excellent tool for people who are either trying to conceive or those that are avoiding pregnancy.
By creating a clearly outlined menstruation calendar, this app could be used to eliminate uncertainty centered around the date of one's period.