Twitter Card Module
This module in short, grabs the article and turns it into a Twitter Card compatible website by using your website, current URL, metadescription to improve your Twitter outreach and also works as an addition to metadata which is great for search engine opitimization. So what do you get? You'll get the module which is pretty much self explanitory providing you know your way around Joomla.
Can I see a demo?
Sure you can. It's hidden within the view source so right click and view source to see it that way. Alternatively to check that the module is working grab the URL in your browser and enter it in the Twitter Card Testing Tool here.
Will my Joomla installation run it?
If you're using either Joomla 2.5 or Joomla 3.0 this will work straight of the bat. That's not to say you can't download it and modify it for use.