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 Golfig AB:
Swing it Viewer is a free application to view Swing it documents created by Swing it or Swing it Pro. This application is intended for the students that have received a Swing it Document from their instructor. Please not that this application cannot open movie-files. You cannot make any drawings on-top of the movie with this application! Highlights include * Unlimited number of movies displayed simultaneously (restricted by screen size and CPU) * Video windows can be made semi-transparent so it's easier to compare swings * Playback at any speed * Play/step/scrub all movies simultaneously * Slow-motion movies handled * Tempo / rhythm information (if set in Swing it / Swing it Pro)