ada is a compact twitter client running on Adobe AIR. The interface is very minimal and the basic feature set is tucked away by default and revealed when you hover over a tweet. RT, reply, and favorite buttons appear on the right side of each tweet. Otherwise, the interface is similar to an IM window. In the lower left of the window there is a filter box for usernames. Typing just a few letters of any username you follow will give you a list of their recent tweets.
Selective Twitter Status is a Facebook Application that lets you decide when to post Twitter updates to Facebook by including a #fb hashtag at the end of your tweet. Many Facebook users get confused or annoyed by the volume of status information a regular tweeter broadcasts. Running this app allows both parties to remain happy instead of endlessly insulting the other faction with wild, emotional attachment to their platform of choice.
This Facebook app cannot work if your updates are protected. It has no password integration.
TwInbox was originally named OutTwit. It is an Outlook plugin that integrates Twitter into the Outlook interface. From the TwInbox website:
Bitter is a lightweight Twitter client built on .NET, so it's Windows only. From the Bitterware site:
It consumes a low amount of memory, is theme-able, is secure (uses HTTPS for authentication and encrypts authentication details), uses a familiar tabbed-interface and so much more!