I've always found the story of the early days of the PC industry to be extremely interesting.  One reason for this is that I experienced those early days myself.  I have my own memories of them.  Another is that the PC's eventual rise to prominence is the stuff of movies.  When the PC was first released, almost no one foresaw the way it would come to dominate the world of computing in such a relatively short period of time.  All "serious" programming was done on bigger boxes. 

One reason the PC grabbed the foothold it did and later exploded on to the scene is the invention of the spreadsheet -- the first "killer app."  The original spreadsheet for the PC was called VisiCalc and was invented in 1978-79 by Dan Bricklin and Bob Frankston.  Rather than being a screen-oriented, essentially non-interactive app as most mainframe apps were at the time, VisiCalc was character-oriented and completely interactive.  It leveraged the basic interactivity of the PC and, at the same time, demonstrated that the PC was a real computer.  Minis and mainframes tried for years to recover the ground they'd lost in this area, but most eventually gave up.

Dan went on to found Software Garden and produce the Dan Bricklin's Demo app, with which I'm sure many of you are familiar.  He's one of my heroes and certainly has his place in the history of our industry.  To see his recollection of those early days and take a trip down memory lane (for you old fogies out there), visit his history page here.  If you'd like to revisit what software was like back in the old days, grab a copy of the PC version of VisiCalc here.