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 Translucent Software:
Translucent provides detailed real-time information about what is going on inside your Mac. At any given time Translucent displays how much each one of your processors is being utilized, detailed information about how your memory is being used, how much data is being sent and received on your network interfaces and how much is being read and written to your hard disks. It displays itself as small addition to your status bar with tooltip-style detail popups; displaying more detailed information on any of the sensors in the status bar. Translucent also displays its sensor information in windows for larger and more detailed information viewing.