When I saw the "first killer app" headline I immediately thought "VisiCalc". I used it ad-nauseum on a TRS-80 III as a neuroscience lab assistant in the early '80s. Before I got that software I used actual paper spreadsheets, either big 17"x11" sheets, or painfully self ruled paper. After enough hours of that I carried my TRS-80 into the lab and introduced my professor to it and VisiCalc, who fell in love and bought one for the lab.

If you've never spreadsheeted on paper you may not realize the glory of even the most primitive spreadsheet app. I used to use erasers until my fingers went numb or white-out by the quart.

Up hill both ways. You young whippersnappers have no idea how good you have it.

I sat with the prof to show him my first attempt, with a half dozen formulas in it. He looked over my shoulder and showed me that every. fucking. formula. was wrong. I felt humiliated. But we fixed them as we went, and watching the changes flow into the cells was magic. My force had been multiplied.

The skills from VisiCalc have transferred to other spreadsheets over the years very well. It's amazing how much Mr. Bricklin got right. I wonder how much was his brilliance and how much was the inevitability of the design.