Tweetie for Windows

NO, it’s not (though I wish).  It is however the nearest thing.  It’s called blu.  Get it here: http://www.thirteen23.com/experiences/desktop/blu/#

It is beautiful in Vista & 7.  Much like Tweetie, you have simple selections for favs, directs, mentions, etc.  The animations for moving to the settings feels a lot like the attention to experience you get in Mac programs (very nice).