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 Mate Farkas:
A must-have app for CCTV Professionals. This easy to use app helps to calculate the required storage space for a CCTV system. You can use it for your DVR or NVR, independent from brands. It helps to calculate the storage requirements for any surveillance system. Simply select how many cameras to record, adjust the the bit rate and choose how many days to record. Additionally you can consider using motion detection by estimating the amount of movement. You will get immediately the required storage space for your CCTV system. The app can be used for any DVRs or NVRs like Dedicated Micros, Dallmeier, Exacq, Hikvision, Milestone, Pelco, etc.