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 Millhouse Engineering:
Roman Calculator is a full function calculator and the first to calculate roman fractions. The graphics are optimized for ipod touch, iphone and ipad. Choose from four backgrounds including your image library and five button style. Styles are selectable in preferences or can be set with a left or right swipe. The result of all calculations will be displayed as a roman number. Tap the Convert button to convert Roman to Arabic and visa versa. In landscape mode, both roman numbers and arabic numbers are displayed. Landscape mode also adds more functions. The functions include sin, cos, tan, square root, inverse, memory and more.