TweetDeck is an application that brings you several Twitter tools in one integrated client. Within TweetDeck, you can manage the people you follow, send tweets and direct messages, follow any @ replies or mentions, and much more.
If you access Twitter from its original interface on the Twitter Web site, you need to refresh the page every time you want to see updates. Instead, TweetDeck feeds you those updates as they come in. When someone you follow posts a new tweet or you receive a reply, a beep or visual flag will notify you. TweetDeck also runs independently of your Web browser.
The big draw of TweetDeck is its ability to organize your list of contacts into a column-based format. This is especially helpful if you follow a lot of people. By setting up groups, you can manage your contacts in any way you choose. For example, if you follow stand-up comedians on Twitter, you can set up a "comedian" group, which will allow you to view a column of comedian-only tweets. TweetDeck also lets you click on a user name to find out more information about that person.
Other little goodies in TweetDeck include an automatic URL shortener (invaluable when you're working with only 140 characters), a feature called TweetShrink which will help you reduce a too-long tweet, a shortcut to image and video uploads, and a button that allows you to also send your tweets to Facebook.
All these features work to assist you in managing your Twitter feed in a much more efficient way.