Yes, another Twitter client (I'm cdevroe by the way). However, this one comes from atebits - the company that brought us the highest ranked Twitter client for the iPhone, also named Tweetie.
Tweetie for Mac, which I've been using all morning, allows for multiple accounts, posting from the browser, auto URL shortening, and much more. Although it feels like 1.0 it is certainly a well polished 1.0. Looking forward to watching this application mature.