Killer application

One mark of a good computer is the appearance of a piece of software specifically written for that machine that does something that, for a while at least, can only be done on that machine.

— Steven Levy, 1985[4]

VisiCalc, the earliest generally agreed-upon example of a killer application

One of the first recognized examples of a killer application is generally agreed to be the VisiCalc spreadsheet for the Apple II series.[4][5] Because it was not available on other computers for 12 months, people spent $100 for the software first, then $2,000 to $10,000 on the Apple computer they needed to run it.[6] BYTE wrote in 1980, "VisiCalc is the first program available on a microcomputer that has been responsible for sales of entire systems",[7] while Creative Computing's VisiCalc review was subtitled "reason enough for owning a computer".[8] Others also chose to develop software, such as EasyWriter, for the Apple II first because of its higher sales, helping Apple defeat rivals Commodore International and Tandy Corporation.[6]

Lotus 1-2-3 similarly benefited sales of the IBM PC.[4] Noting that computer purchasers did not want PC compatibility as much as compatibility with certain PC software, InfoWorld suggested "let's tell it like it is. Let's not say 'PC compatible,' or even 'MS-DOS compatible.' Instead, let's say '1-2-3 compatible.'"[6][9] Another killer app is WordStar, the most popular word processor during much of the 1980s.[10]

The UNIX Operating System served as a killer application for the DEC PDP-11 minicomputer and VAX-11 minicomputer during roughly 1975–1985. Many of the PDP-11 and VAX-11 processors never ran DEC's operating systems (RSTS or VAX/VMS), but instead, they ran UNIX, which was first licensed in 1975. To get a virtual-memory UNIX (BSD 3.0) you had to purchase a VAX-11 computer. Many universities wanted a general-purpose timesharing system that would meet the needs of students and researchers (early versions of UNIX included free compilers for C, Fortran, and Pascal; at the time, offering even one free compiler was unprecedented). From its inception UNIX could drive high-quality typesetting equipment and later PostScript printers using the nroff/troff typesetting language, and this was also unprecedented for its time. UNIX was the first operating system offered in source-license form (a university license cost only $10,000, less than a PDP-11), allowing it to run on an unlimited number of machines, and allowing the machines to interface to any type of hardware because the UNIX I/O system was extensible.

The first recorded use of the term in print was 1988, in PC Week 24 May. 39/1. "Everybody has only one killer application. The secretary has a word processor. The manager has a spreadsheet."[11]

The definition of "killer app" came up during Bill Gates's questioning in the United States v. Microsoft Corp. antitrust case. Bill Gates had written an email in which he described Internet Explorer as a killer app. In the questioning, he said that the term meant "a popular application", and did not connote an application that would fuel sales of a larger product or one that would supplant its competition, as the Microsoft Computer Dictionary defined it.

Introducing the iPhone in 2007, Steve Jobs said that "the killer app is making calls."[12] Reviewing the iPhone's first decade, David Pierce for Wired wrote that although Jobs did indeed prioritize a good experience making calls in the phone's development, other features of the phone soon turned out to be more important, such as its data connectivity and ability to install third-party software (which was added later).[13]

• Disruptive innovation
• Killer feature