TweetDeck, which has been owned and operated by Twitter itself since mid 2011, is closing down its Android and iPhone apps to focus on future development of its web app. The app itself hasn't seen an update or redesign in the Play Store since the end of 2011, but other developers have built on top of TweetDeck for much longer. In a post on its official blog, TweetDeck says that it will discontinue support for the apps in May by pulling them from their respective stores, and the apps will stop working short after. Some of the "blame" is put on Twitter's upcoming retirement of the v1.0 API, which the apps rely on, but it's a much bigger story than that.
This shutdown should come as no surprise considering the stagnation in development of the app and Twitter's move to cut down on third party Twitter client development. TweetDeck says as much in its post, where it notes that it has made "an increased investment in Twitter for iPhone and Twitter for Android", and that the combination of a better official Twitter app along with improvements to the TweetDeck web app will improve the experience for users.