Our industry stands on the shoulders of VisiCalc, the genius creation of Dan Bricklin and Bob Frankston. VisiCalc, short for visible calculator, was a "magic sheet of paper that can perform calculations and recalculations."
VisiCalc was the first spreadsheet software for personal computers. Originally released for the Apple II, it helped turn the microcomputer from a hobby device for enthusiasts into a serious business tool. VisiCalc is considered the Apple II's killer app, selling over 1 million copies.
Thank you Dan and Bob!
(Read more on Wikipedia)