killer app
n. A technology so compelling that it drives the sales of, or leads to widespread adoption of, related technologies.
A killer app is more than just a best-selling software program. Rather, it is a program that is so popular and presumably so necessary that it causes people to buy the hardware it runs on. For example, Windows 95 could be considered a killer app because it caused people to buy new PCs that supported the operating system. A lot of analysts are waiting for a killer app to be developed for handheld PCs, which would spur sales of those devices and bring them more into the mainstream.
—Tamara E. Holmes, “Beware the killer app: It'll make you spend more money,” USA Today, January 13, 1999
Most recently, the World Wide Web has been called the killer app for the Internet, making it essential. And the Internet itself has been called a killer app, validating the concept of computer networks.
—Dwight Silverman, “'Killer app' apt to be nothing really special,” The Houston Chronicle, November 27, 1998
1988 (earliest)
Part of the conventional wisdom on why Corporate America fis taking so long to come around on OS/2 has to do with the famous "Killer Apps" theory.

Until we see those first two or three killer apps, this theory goes—and by "killer apps" most people mean new programs, written to run only under OS/2, which are profoundly better than anything available under DOS—few corporate customers will see much reason to begin to commit to OS/2.
—Jim Seymour, “'Killer Apps' theory doesn't sway big business,” PC Week, May 24, 1988
Some Related Words