TwitterCal is a free service that helps you in integrating your Tweets with Google Calendar. To add an event to your Google Calendar, you can just send a tweet with details of the event, and TwitterCal will automatically add it to your Google Calendar. It is as simple as that.
I had recently reviewed some applications that make a very ingenious use of Twitter, like TweetWhatYouSpend, TweetMyPC, and TrackThis. TwitterCal is another useful application that makes a very unique use of Twitter API.
TwitterCal is completely free. To start using TwitterCal, you provide it your Twitter username, and then authenticate it to use your Google Calendar (they don’t store your password). After that, you follow gcal on Twitter. [subscribe-to-us]
Whenever you want to add a new event to your Google Calendar, you just send a direct message to TwitterCal. It will send that to Google Calendar using Google’s Quick Add feature. You can include all the details of your event (date, time, name) in your tweet in natural language form, and Google Calendar automatically interprets that, and add that as an event.
TwitterCal is a very intelligently made service. If you want to maintain a Todo List using Twitter, you can try ToDoTweet.