You find a bug in macOS or iOS. Something in the software isn’t working the way it should work. You decide to let Apple know, and head over to http://
bugreport.apple.com and login with your Apple ID. You fill out the required form, list the reproduction steps, hit the special key chord to generate a fat sysdiagnose, attach some screen shots, and hope they fix it.
"VisiCalc" was the catalyst, the era's killer application, that made the development of the Lisa and then the Macintosh possible. Looking back at the critical role the world’s first spreadsheet "VisiCalc" had on Apple’s early success.