My Doctor always asks "Date of you last period?" and for the first time ever in my life I could answer it accurately thanks to My Days. If you are a Mother with daughters and keep track of that sort of thing, you can have multiple accounts on one phone to track them. I also like how you can add Notes to any day here. The only thing I can think that would make it better is adding a subtle note to Google Calendar!
Phone Tested On: Nexus One
Developer: Christian Albert Mueller