Twittereeze is a SIMBL (Smart InputManager Bundle Loader) extension for Twitterific (freeware), a Mac OS X client for the Twitter service. Twittereeze aims to improve Twitterific's user experience in small ways.
While Twitterific itself is a nice little app to send and receive 'tweets', i.e. change your own status and stay up-to-date on that of others, I primarily use Twitter in a similar manner to an IM network's status message. Thanks to AppleScript, the status messages of iChat (AIM/.mac/ICQ, Jabber/Google Talk/LiveJournal), Skype and Adium (many, many protocols) can be changed through a simple API. With Twittereeze enabled, any status that Twitterific sends to Twitter as a 'tweet' automatically becomes your status on those three applications as well, provided you have them running.
Moreover, Twittereeze makes the 'What are you doing?' text field frontmost (except when it doesn't make sense), so you can typically type right away, and it adds the following keyboard shortcuts:
In a nutshell, it eliminates many, many cases of having to unnecessarily switch between keyboard and mouse to use the interface.