I was just reading this, and this paragraph struck my eye:
"Bricklin and Frankston recalled that their initial efforts to promote VisiCalc did not meet universal enthusiasm. Experienced computer people weren’t bowled over, Bricklin said; they would dismiss the spreadsheet with, 'Hey, I can already do most of this in BASIC.' People who had no experience with computers tended to think that computers could do anything under the sun, and so VisiCalc didn’t wow them. 'But when the accountants saw it - there was an accountant [at a particular computer store], he started shaking - he said, ‘This is what I do all day!'"
I would be tempted to call it "The Killer App". By putting computers in the hands of the people who hold the purse-strings VisiCalc made them business necessities in a way no other App has.
"Bricklin and Frankston recalled that their initial efforts to promote VisiCalc did not meet universal enthusiasm. Experienced computer people weren’t bowled over, Bricklin said; they would dismiss the spreadsheet with, 'Hey, I can already do most of this in BASIC.' People who had no experience with computers tended to think that computers could do anything under the sun, and so VisiCalc didn’t wow them. 'But when the accountants saw it - there was an accountant [at a particular computer store], he started shaking - he said, ‘This is what I do all day!'"
Reminds me: who are you solving the problem for?
For more details, here's Bricklin's Visicalc history. http://www.bricklin.com/history/intro.htm