Macworld has the details behind the Tweetbot for Mac release.
Tweetbot for Mac
Yay!
This is a public alpha. There are bugs, crashes, and incomplete features. We are looking for brave souls to help us shape Tweetbot into a fine Twitter client for the Mac.
Tweetbot for Mac confirmed as first image surfaces on Twitter
Can't tell much from this photo, but I'm looking forward to giving it a try.