Scalare (formerly Scalaris) is a minimal and elegant Twitter client.
Scalare (formerly Scalaris) is a Twitter client built as minimal and unintrusive as possible. It shows your friend's tweets as Growl notifications.
Scalare is built with simplicity in mind. It is meant for the casual twitter user that doesn't want to be distracted too much. It has a windowless UI because that's how, according to the developer's opinion, Twitter should work; minimal messages you read and keep going. Feel like sending a tweet? Just press the easy key-combo, type what's in your mind, and you are back to work.
It allows you to send tweets without stopping your workflow. And because Scalare uses Growl, the customization options are endless. Go into System Preferences and set your custom display styles under the Growl preference pane.