Twitter

Twitter is a free social messaging utility for staying connected in real-time.
Why do so many people seem to like Twitter? Simplicity has played an important role in Twitter's success. People are eager to connect with other people and Twitter makes that simple. Twitter asks one question, "What are you doing?" Answers must be under 140 characters in length and can be sent via mobile texting, instant message, or the web. Twitter's core technology is a device agnostic message routing system with rudimentary social networking features. By accepting messages from sms, web, mobile web, instant message, or from third party API projects, Twitter makes it easy for folks to stay connected.