Are you on Facebook, Myspace, Friendster or other social network sites?  This new blogging site got its own way to get users by the simple one question " What are you doing?" Twitter is a free social networking and micro-blogging service that enables its users to send and read other users' updates known as tweets. Tweets are text-based posts of up to 140 characters in length which are displayed on the user's profile page and delivered to other users who have subscribed to them (known as followers). Senders can restrict delivery to those in their circle of friends or, by default, allow anybody to access them.