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 Poets Mobile:
Official app for the Feature Film: Piranha 3D. This is the first app in actual 3D! Put on 3D glasses and watch the interactive piranhas pop out at you! Immerse yourself inside two different piranha packs: Prehistoric piranha from the movie Piranha 3D, and real life Red Bellied piranha. Use your finger to rotate around the pack in a matrix like movement. Just don't get bitten! Meet the cast of the movie, learn real piranha facts, watch videos, and much more! You'll be blown away by the 3D imagery from 3D2Go by Poets Mobile ... Official website of the movie: www.piranha-3d.com - -- Requires OS 4.0 -- Apple is not a sponsor of, or responsible for conducting, the promotion of the Free 3D Glasses available through the app.