TweetDeck by Twitter

TweetDeck by Twitter screenshots

It helps you build custom Twitter timelines on your Mac.
Posting New Tweet
TweetDeck by Twitter 3.9 : Posting New Tweet

Alternative downloads

Social for Facebook
2.0.8
This application allows you to check your Facebook account from your desktop.
Twitter Automator Action Pack
1.02
FREE
This action pack extends the power of Automator in Leopard with 10 actions.
Nocturn
1.6.6
FREE
Manage multiple Twitter accounts and read and post tweets in your timeline.