X (Twitter) - Connect with your friends and other fascinating people. Get in-the-moment updates on the things that interest you. And watch events unfold, in real time, from every angle.
Twitter Bookmarks - Create shortcuts to your favorite users/tweets on Twitter
Tweetflick - Save, organize & find Tweets to get the most out of Twitter
Twitter Bots - Make smart Twitter bots without coding
TweepsBook - A better bookmarking tool for power Twitter users that you can use to filter, organize and bookmark tweets on your liking.
isit100.com - The simplest way to get feedback from your friends