VisiCalc

First Spreadsheet for a Personal Computer.

Conceived by Dan Bricklin, refined by Bob Frankston, developed by their company SoftwareArts, and distributed by Personal Software in 1979 (later named Visi Corp) for the Apple II computer, it propelled the Apple from being a hobbyist's toy to being a much-desired, useful financial tool for business.

http://en.wikipedia.org/wiki/VisiCalc