I understand how to create a custom TAB, but wondering what they used to create the webpage within. Is it a third party script provided somewhere? A wordpress plugin? or just plain jane HTML code that someone wrote specifically for the site?
If you scroll over the links you'll see that they relate back to an offsite script hosted by the page owner. There's no immediate mention of a 3rd party app but it could just as easily be a precanned solution as a custom one.
In either case since an iFrame is pulling in external content you're really only limited by the width of the page, the facebook terms and any integration you may want through Facebook connect. Otherwise it's just a webpage.