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 The Appstillery Ltd.:
MapMatcher San Francisco takes mapping to the next level, allowing you to explore the same area on up to four maps at a time on your iPad. As you move about one map, so the other maps all keep in sync. Ever wanted to compare two maps? Ever wondered how the city's landscape has changed throughout history? How the metro map compares to reality? MapMatcher uses MakkaMappa technology and is a great way to experience the amazing way that MakkaMappa can turn any image into a GPS map. You can even import maps you've made on MakkaMappa.com for free! Display up to four maps (including the satellite view) on the screen at once. 10 maps are built into the app. Download more maps for free in the future. Find over 20 of San Francisco's most famous landmarks. See your own position on any of the maps. Import maps you've made on MakkaMappa for free. The maps that come with the app include: San Francisco in 1887 San Francisco in 1896 Bay Area 1926 Two maps of the 1939 Golden Gate International Expo (on Treasure Island) San Francisco in 1953 Alcatraz Island Presidio Fort Mason Municipal RailwayWe will be adding more maps to the app and these will appear as free available downloads within the app.