It isn’t obvious to anybody who has lived in a world where PCs, mobile phones, the Internet, broadband and iPods are just part of the fabric of life, but there was a time when people were not sure what value a personal computer represented, or what one could do with such a device. 

The killer app, as it turns out, was the spreadsheet, which quickly became the reason financial and accounting types quickly adopted the new technology. 

For better or worse, it is the software that has given everyone the means to play with numbers and ask, “What if?”

But killer apps have driven the adoption of many other products. One might argue that a killer app must be perceived before any innovation gets traction. That's just another way of saying a product has to have obvious value and a use case before most people are persuaded to buy or use them. 

So the spreadsheet was the killer app that drove PC adoption by some business users. Word processing then became the app that made PCs useful for a wider range of office employees, college professors and students. One might argue it was desktop publishing that made Apple the essential tool for many graphic arts personnel. 

The ability to have a phone conversation anyplace was the killer app for mobile phones. PC dongles and smartphones supporting Web access and applications arguably were the killer app for third-generation mobile networks. 

E-mail was the killer app for dial-up Internet access, while the World Wide Web played a similar role for fixed broadband.

One of the first examples of a killer application is generally agreed to be theVisiCalc spreadsheet on the Apple II platform.

Lotus 1-2-3 spurred sales of IBM's "PC" as well.

Aldus PageMaker and Adobe PostScript gave the graphic design and desktop publishing niche to the Apple Macintosh in the late 1980s.

It seems fairly clear that "reading" is the killer app for an e-reader, though it is not yet clear what killer app might develop for the tablet PC. Likewise, we cannot yet say what killer app might emerge for fourth-generation wireless networks.