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 Paul Gardiner:
This is the ad-sponsored, but fully functional, free version of CalculateThis! CalculateFree! is an easy to use yet powerful calculator, that can be used for everything from adding up your grocery bill, to performing complex scientific calculations. You enter equations as you would write them, and calculate this shows you the answer, and the input, as you write it. Equations are shown in an easy to read graphical format, and you can make corrections as you go. There are also multiple color themes to choose from, so you can personalize your calculator. CalculateFree! includes standard memory functions, plus an innovative history list is kept of recent calculations. This allows you to include a recent result in a new calculation, or return to an item from the history to modify the equation. CalculateFree! includes the following functions: - square root, cube root, and nth root - squared, cubed, and x to power y - constants for phi, pi, and e - log (base 10, base e, and base y) - Memory +/-/recall - factorial - C(n,r) - r combinations of n - P(n,r) - r permutations of n - percent - sin, cos, tan, and inverses - hyperbolic trigonometric functions and inverses - degrees and radians for trigonometric functions