Twitter clients, websites and web apps

A variety of applications, websites, and web applications have been built to make Twitter more useful .  For instance, Twendz can show you the overall sentiments on a topic, Twellow is a directory of people on the Twitter platform and can help you discover people to follow, etc.  We are building a directory of applications for your reference.  If you have any suggestions for applications you would like us to add, please let us know.