The 3.18 version of TweetDeck for Mac was available to download on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The program lies within Lifestyle Tools, more precisely Entertainment. The actual developer of this free Mac application is Twitter, Inc. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe.
From the developer:
TweetDeck makes it easier for publishers, marketers and power users to track the real-time conversations they care about. And, you can join the conversation by tweeting, sharing photos and links to news stories, and more. It brings more flexibility and insight to power users through a customizable layout that lets you keep up with the people and topics that matter most to you.
You may want to check out more Mac applications, such as TweetDeck by Twitter, BetterTDeck for TweetDeck or Tweeten, which might be related to TweetDeck.