Apple II
AppleWorks on the Apple II
1984 not only brought us the Mac, it brought us an 8-bit app that made it easy to resist purchasing a Mac.
spreadsheet
spreadsheet
Lotus 1-2-3 on the PC w/DOS
VisiCalc started it, but 1-2-3 finished it. "It" being the discussion of what a spreadsheet can be, and also VisiCalc itself.
spreadsheet
VisiCalc on the Apple II
In 1978, Bricklin and Frankston took out a loan to develop "Calcu-ledger," a tool that could project the fiscal health of taking out that very loan