Update 2013-12-12: I received information from Paul Annett (@paulannett, that TweetDeck is very much alive:
The screen capture is from TweetDeck, so proof. Note that I missed the news by half a year. I need to use Twitter more.
The previous version was developed in Adobe Air as indicated below. The new version is a Web app. It works reasonably well also on mobile devices, via responsive design, but I wish there was a one screen dashboard, and native apps (hybrid) for at least iOS and Android.
Twitter will close down all versions of TweetDeck, reasons claimed to be Adobe Air going out of fashion and that TweetDeck is not updated to the latest Twitter API. Sounds like bad excuses to me, considering TweetDeck is a rather simple application, so it would be easy to rewrite it in Java (making it platform independent) and to update it API-wise. I need to do the latter now and then for Twitizer, BabbleBox etc, and that’s no rocket science. Surely Twitter employees could do that in a shorter time than me. They designed the API!
A year or so ago Twitter acquired or banned some other clients, mainly mobile ones.
Some might consider this trend bad, and Twitter’s terms seemingly indicate that third party clients are not wanted, but in my opinion it rather leaves the field open for apps that e.g. can spot interesting news based on user preferences, using AI, natural language processing etc, or draw conclusions from fire hose analysis about trends, and guess ahead on elections etc, and for that matter very user-friendly mobile apps.
Twitter is seemingly against evolution of its service. It took several years to add support for pictures and ads, and overall not much seems to happen overall, which is also positive for third party.
For the time being the Twitter API is completely open, yet with volume restrictions and such, so it’s still an opportunity for would-be entrepreneurs to exploit the massive reference and opinion database Twitter is.