Visicalc intrigues me because it seems like one of the few apps that seems inevitable, but still revolutionary. Once we had computers it just made perfect sense to have them fill out spreadsheets for us.<p>It's also one of the few digital products that has almost entirely overwritten memory of its predecessor. Digital books haven't made us forget about physical ones. Online encyclopedias haven't erased libraries. But when you ask someone to make a spreadsheet, they will of course think of an excel sheet.