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 The New York Public Library:
Embark on an adventure at The New York Public Library. Inside the Stephen A. Schwarzman Building are 100 powerful objects that have changed history. Unlock maps to each Artifact, learn their stories, and scan them with your camera to activate their special Powers. Collect their Powers by touching and holding your screen. Watch your Powers grow -- and finish your adventure online, where the 100 Artifacts you find at the Library can help you write and publish your own worldchanging Epic. This app works with the online game Find the Future at NYPL: The Game available at http://game.nypl.org.