Twitter is in talks to purchase TweetDeck Inc. for $50 million, according to the Wall Street Journal . TweetDeck is one of the most popular third-party Twitter clients, available in desktop, iPad, iPhone and Android versions. It displays your Twitter news feed, @mentions and direct messages, along with your Facebook feeds — all on the same screen, all updating in real time. TweetDeck can also support updates from MySpace, LinkedIn and Foursquare. The 15-person company, based in the U.K., has never revealed how many users TweetDeck has. The number may be small — but it is also likely to include the most obsessive power users in social media. The report comes days after CNN reported that UberMedia, the company behind Twitter clients Echofon and Twidroyd, was working on a potential Twitter competitor