a users personal calendar

I need to find a calendar that I can use as a plugin

I want to have a calendar that each user on the site will have in their own profile I need the calendar to work like a timed life line where they can post stuff of their own calendar to help them remember what they need to do on that day to do it, I will also like to have it where when they signin it will notify them that something they posted in the calendar is coming up (like a reminder) if anyone know where I can find something like that I would appreciated very much..