The First Killer App: VisiCalc
Sabah Arif writes "The first electronic spreadsheet, VisiCalc, helped transform the Apple II from a home computer into a business computer. Without VisiCalc, it is possible IBM would not have introduced the IBM PC in 1981. Read about the software at VisiCalc's creator Dan Bricklin's site and a brief history at Braeburn."
http://www.bricklin.com.nyud.net:8090/
You can download VisiCalc from here.
http://www.bricklin.com/history/vcexecutable.htm
It is 17K compressed (26K executable).
and does most of what I do with modern spreadsheets (I am a very light user of spreadsheets).
LOL