The "Download Now" link directs you to the iTunes App Store, where you must continue the download process. You must have iTunes installed in order to open the link, and you must have an active iTunes account to download the application. This download may not be available in some countries.
From Taggart Gorman:
The TokinaLenses app is a guide to Tokina's current and past lineup of auto focus lenses for Nikon, Canon, Minolta and Pentax digital and film SLR cameras.You can view all the lenses at once or you can view lenses in a selected category. You have the ability to sort by aperture, minimum focal length and average street price (for currently available lenses).Each lens has a detail page which provides links to the Tokina web page detailing the lens and reviews of the lens from third parties (if available - brand new lenses might not have reviews yet).Please note that Tokina at times has released several versions of the same lens with slightly different statistics. I have drawn the list of lenses directly from Tokina's website, so if there is a lens missing, you need to bring it up with Tokina! :-)