I would praise Google Calendar as one of the best Calendar, TODO, GTD( Get Things Done ) , Micro Journal kind of application that I’m using for a quite long time.
Google Calendar lets you to create events future or past and make the event to be reminded at a given interval. Google Calendar communicates the event through various means of communication. i.e through Email, through SMS and even Popup Message in the system if your event is a short period.
Also you can change the view of your calendar as Daily, Weekly, Monthly and Agenda format to view and organize the items. Also it lists down the events of Next 7 Days.
Google Calendar allows you to publish your calendar and you can mark which group of items can be published. So this helps to keep others updated of my schedule and common friends birth day.
Google Calendar has become my integral part of my life as it used as my Micro Journal, which records my personal and life’s event and cheries my life when I look back at it!!! :-)