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 J Doorneweert:
Week numbers are used in a lot of things. In school, in business, for holiday planning and deliveries. This Week App shows the current week, and day.You can also use it to find out on which day you were born, or on which day your birthday is.Whether the week starts on sunday or monday is determined by the setting selected in Region Format. For example, if your current selection is Netherlands, or United Kingdom the week will start on a monday, if your current selection is United States, the week will start on a Sunday. This setting is found in: Settings>General>International>Region Format.