In marketing terminology, a killer application (commonly shortened to killer app) is any computer program or software that is so necessary or desirable that it proves the core value of some larger technology, such as computer hardware, a video game console, software, a programming language, a software platform, or an operating system. In other words, consumers would buy the (usually expensive) hardware just to run that application. A killer app can substantially increase sales of the platform on which it runs.
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.
One of the first recognized examples of a killer application is generally agreed to be the VisiCalc spreadsheet for the Apple II series. 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. BYTE wrote in 1980, "VisiCalc is the first program available on a microcomputer that has been responsible for sales of entire systems", while Creative Computing's VisiCalc review was subtitled "reason enough for owning a computer". Others also chose to develop software, such as EasyWriter, for the Apple II first because of its increasing sales.
Lotus 1-2-3 similarly benefited sales of the IBM PC. 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.'" Another killer app is WordStar, the most popular word processor during much of the 1980s.
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."
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." 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).
The term has also been applied to computer and video games that persuade consumers to buy a particular video game console or other video game hardware product over a competing one, by virtue of being exclusive to that platform. Such a game is also known in video game parlance as a "system seller". Examples of video game killer applications include:
- Space Invaders, originally released for arcades in 1978, became a killer app when it was ported to the Atari VCS console in 1980, quadrupling sales of the three-year-old console.
- Star Raiders, released in 1979, may have been a system-seller for the Atari 400/800 computers. Another was Eastern Front (1941), released in 1981.
- In 1996, Computer Gaming World wrote that Wizardry: Proving Grounds of the Mad Overlord (1981) "sent AD&D fans scrambling to buy Apple IIs".
- The Famicom home port of Xevious is considered the console's first killer app, which caused system sales to jump by nearly 2 million units.
- The video game website GameTrailers considers the Super Mario Bros. games to be the killer app for nearly all Nintendo home consoles, Tetris as the killer app for the Game Boy, Grand Theft Auto III for the PlayStation 2, Super Smash Bros. Melee for the Nintendo GameCube, and Wii Sports for the Wii.
- Computer Gaming World stated that The Legend of Zelda on the Nintendo Entertainment System, Phantasy Star II on the Sega Genesis, and Far East of Eden for the NEC TurboGrafx-16 were killer apps for their consoles.
- The Super Mario, Final Fantasy, Dragon Quest games were killer apps for Nintendo's Famicom and Super Famicom consoles in Japan.
- John Madden Football's popularity in 1990 helped the Genesis gain market share against the Super NES in North America.
- Sonic the Hedgehog, released in 1991, was hailed as a killer app as it revived sales of the (by then) three-year-old Genesis. 
- Mortal Kombat helped pushed the sales of the Genesis due to being uncensored unlike the Nintendo version.
- Streets of Rage was a system seller for the Mega Drive/Genesis in the UK.
- Street Fighter II, originally released for arcades in 1991, became a system-seller for the Super NES when it was ported to the platform in 1992.
- Myst and The 7th Guest, both released in 1993, drove adoption of CD-ROM drives for personal computers.
- Virtua Fighter and Sakura Wars were considered crucial to the Sega Saturn's success in Japan.
- Euros 96 was a major system-seller for the Sega Saturn in the United Kingdom.
- Sega Rally Championship was another major system-seller for the Sega Saturn in the United Kingdom, becoming the fastest selling CD game at the time. 
- Die Hard Arcade and Fighters Megamix boosted the Sega Saturn's sales in the United States.
- In the early lifespan of the original Sony Playstation, games like Ridge Racer, Battle Arena Toshinden, Wipeout, Resident Evil, Tomb Raider and NFL GameDay were considered its killer apps.[a]
- The Tekken and Grand Theft Auto games were killer apps for the Sony PlayStation and PlayStation 2 consoles.
- Super Mario 64, as well as GoldenEye 007, were considered killer apps for the Nintendo 64.
- Virtua Fighter 3 was the killer app for the Sega Dreamcast in Japan.
- Halo: Combat Evolved and Halo 2 are considered the killer apps for the original Xbox, and the subsequent series entries went on to become killer apps for the Xbox 360 and Xbox One.
- Blue Dragon served as a killer app for the Xbox 360 in Japan.
- Metal Gear Solid 4 caused a boost in PlayStation 3 sales.
- Super Mario Galaxy and its sequel were acclaimed as killer apps for the Wii. 
- Bloodborne was known as the first killer app for the PlayStation 4 console.
- The Legend of Zelda: Breath of the Wild was the killer app for the Nintendo Switch console.
- Half-Life: Alyx was considered a killer app for virtual reality headsets, on account of being thought of by many as the first true AAA virtual reality game. Sales of VR headsets — such as the Valve Index — increased dramatically after its announcement, suggesting users bought the product specifically for the game.
- "Killer app". Merrian-Webmaster. Merriam-Webster, Incorporated. Retrieved 14 January 2015.
- Scannell, Ed (February 20, 1989). "OS/2: Waiting for the Killer Applications". InfoWorld. Vol. 11 no. 8. Menlo Park, CA: InfoWorld Publications. pp. 41–45. ISSN 0199-6649. Early use of the term "Killer Application".
- Kask, Alex (September 18, 1989). "Revolutionary Products Are Not in the Industry's Near Future". InfoWorld. Vol. 11 no. 38. Menlo Park, CA: InfoWorld Publications. p. 68. ISSN 0199-6649. Early use of the term "Killer App".
- Levy, Steven (January 1985). "The Life and Times of PC junior". Popular Computing. p. 92. Retrieved 2020-03-12.
- D.J. Power, A Brief History of Spreadsheets, DSSResources.COM, v3.6, 30 August 2004
- McMullen, Barbara E. and John F. (1984-02-21). "Apple Charts The Course For IBM". PC Magazine. p. 122. Retrieved 24 October 2013.
- Ramsdell, Robert E (November 1980). "The Power of VisiCalc". BYTE. pp. 190–192. Retrieved 18 October 2013.
- Green, Doug (August 1980). "VisiCalc: Reason Enough For Owning A Computer". Creative Computing. p. 26. Retrieved 18 October 2013.
- Clapp, Doug (1984-02-27). "PC compatibility". InfoWorld. p. 22. Retrieved 18 January 2015.
- Bergin, Thomas J. (Oct–Dec 2006). "The Origins of Word Processing Software for Personal Computers: 1976-1985". IEEE Annals of the History of Computing. 28 (4): 32–47. doi:10.1109/MAHC.2006.76. S2CID 18895790.
- Earliest usage cited in Oxford English Dictionary
- Newton, Cal. "Steve Jobs Never Wanted Us to Use Our iPhones Like This". New York Times. Retrieved 27 June 2020.
- Pierce, David. "Even Steve Jobs Didn't Predict the iPhone Decade". Wired. Retrieved 27 June 2020.
- "The Definitive Space Invaders". Retro Gamer. No. 41. Imagine Publishing. September 2007. pp. 24–33. Retrieved 2011-04-20.
- Williams, Gregg (May 1981). "Star Raiders". BYTE. p. 106. Retrieved 18 October 2013.
- Greenlaw, Stanley (November–December 1981). "Eastern Front". Computer Gaming World (review). pp. 29–30. Retrieved 31 October 2013.
- "150 Best Games of All Time". Computer Gaming World. November 1996. pp. 64–80. Retrieved 25 March 2016.
- 遠藤昭宏 (June 2003). "ユーゲーが贈るファミコン名作ソフト100選 アクション部門". ユーゲー. No. 7. キルタイムコミュニケーション. pp. 6–12.
- Kurokawa, Fumio (17 March 2018). "ビデオゲームの語り部たち 第4部：石村繁一氏が語るナムコの歴史と創業者・中村雅哉氏の魅力". 4Gamer.net. Archived from the original on 1 August 2019. Retrieved 24 August 2019.
- Adams, Roe R. III (November 1990). "Westward Ho! (Toward Japan, That Is)". Computer Gaming World. p. 83. Retrieved 16 November 2013.
- "The lack of a killer app". Computing Japan. Vol. 36–41. LINC Japan. 1997. p. 44.
Noguchi points out that every time sales of a particular game console have taken off, it has been because it had a new "killer software." Nintendo had Super Mario Brothers, Dragonquest, and Final Fantasy. And Sony PlayStation now has Final Fantasy VII, which has been selling like hotcakes since it was released at the end of January. Total shipments of PlayStation, which numbered 10 million worldwide as of November 1996, had jumped to 12 million by February 14 and 16 million by the end of May.
- Hruby, Patrick (2010-08-05). "The Franchise". ESPN. Retrieved 23 January 2015.
- Fahs, Travis (2008-08-06). "IGN Presents the History of Madden". IGN. Retrieved 2009-03-30.
- Gates, James. "The Creation of Sonic The Hedgehog". Culture Trip. Retrieved 2020-05-21.
- Patterson, Eric L. (November 3, 2011). "EGM Feature: The 5 Most Influential Japanese Games Day Four: Street Fighter II". Electronic Gaming Monthly. Archived from the original on 14 March 2017. Retrieved 17 April 2012.
- "PC Retroview: Myst". IGN. August 1, 2000. Archived from the original on January 20, 2012. Retrieved April 21, 2008.
- "Virtua Fighter Review". Edge. December 22, 1994. Archived from the original on December 10, 2014. Retrieved March 5, 2015.
Virtua Fighter's 3D characters have a presence that 2D sprites just can't match. The characters really do seem 'alive', whether they're throwing a punch, unleashing a special move or reeling from a blow ... The Saturn version of Virtua Fighter is an exceptional game in many respects. It's arguably the first true 'next generation' console game, fusing the best aspects of combat gameplay with groundbreaking animation and gorgeous sound (CD music and clear samples). In the arcades, Virtua Fighter made people stop and look. On the Saturn, it will make many people stop, look at their bank balance and then fork out for Sega's new machine. Over to you, Sony.
- "Tonight We're Going to Party like it's 1996!". Sega Saturn Magazine. No. 16. Emap International Limited. February 1997. p. 10.
- "Sega go to the Top of the Charts!". Sega Saturn Magazine. No. 5. Emap International Limited. March 1996. p. 6.
- Levy, Stuart; Semrad, Ed (January 1997). "Rage Racer". Electronic Gaming Monthly. No. 90. Ziff Davis. p. 112.
- "Top 25 Games of All Time: Complete List". IGN. 23 January 2002. Archived from the original on 4 May 2010. Retrieved 6 January 2012.
- "The Top Ten Most Important Launch Titles Of All Time". Cinema Blend. Future plc. 31 January 2010. Retrieved 17 May 2021.
- Hickman, Sam (March 1996). "The Thrill of the Chase!". Sega Saturn Magazine (5). Emap International Limited. p. 36.
And if there was one game that sold Playstation on launch, it was WipEout
- Leadbetter, Richard (4 December 2014). "20 years of PlayStation: the making of WipEout". Eurogamer. Gamer Network. Retrieved 11 December 2014.
- "NG Alphas: NFL GameDay '97". Next Generation. No. 23. Imagine Media. November 1996. p. 92.
- Blache, Fabian; Fielder, Lauren (31 October 2000). "GameSpot's History of Tomb Raider". GameSpot. Archived from the original on 6 March 2009. Retrieved 1 June 2010.
- "NG Alphas: NFL GameDay '97". Next Generation. No. 23. Imagine Media. November 1996. p. 92.
- Stevens, Chris (4 January 2011). Designing for the iPad: Building Applications that Sell. John Wiley & Sons. ISBN 978-0-470-97693-7.
- Hutchinson, Lee (2013-01-13). "How I launched 3 consoles (and found true love) at Babbage's store no. 9". Ars Technica. Retrieved 2020-06-20.
- "The 52 Most Important Video Games of All Time (page 5 of 8)". GamePro. April 24, 2007. Archived from the original on 4 April 2010. Retrieved 17 May 2021.
- Nicholson, Zy (September 2001). "Final Reality". Official UK PlayStation 2 Magazine (11): 49, 50.
- Craig Glenday, ed (2008-03-11). "Hardware History II". Guinness World Records Gamer's Edition 2008. Guinness World Records. Guinness. p. 27. ISBN 978-1-904994-21-3.
- Sun, Leo (2016-12-15). "Why 'Halo: The Master Chief Collection' Will Save the Xbox One -- The Motley Fool". The Motley Fool. Retrieved 2016-12-15.
- Loguidice, Bill; Barton, Matt (February 24, 2014). Vintage Game Consoles. CRC Press. ISBN 9781135006501. Retrieved June 3, 2020.
- "Hands-on with Super Mario Galaxy". Engadget. Retrieved 2020-05-21.
- Kain, Erik. "'Bloodborne' Review Round-Up: The PS4's First Killer App". Forbes. Retrieved 2016-12-14.
- Craddock, Ryan (3 March 2021). "Anniversary: Nintendo Switch Launched Four Years Ago Today". Nintendo Life. Retrieved 18 April 2021.
- Lawver, Bryan (2021). "All 17 Legend of Zelda games, ranked from worst to best". Inverse.com. Retrieved 18 April 2021.
- Jones, Camden (20 August 2020). "Why Breath Of The Wild Fans Will LOVE A Short Hike". Screen Rant. Retrieved 18 April 2021.
- McKeand, Kirk (23 March 2020). "Half-Life: Alyx review - VR's killer app is a key component in the Half-Life story". VG247. Retrieved 24 March 2020.
- Carbotte, Kevin. "Half-Life: Alyx Gameplay Review: (Almost) Every VR Headset Tested". Tom's Hardware. Retrieved 24 March 2020.
- Robinson, Andrew (23 March 2020). "Review: Half-Life Alyx is VR's stunning killer app". VGC. Retrieved 24 March 2020.
- Oloman, Jordan. "Half-Life: Alyx is a watershed moment for virtual reality | TechRadar". www.techradar.com.
- "CES 2020: Teslasuit Will Unveil New Haptic VR Gloves". Tech Times. 27 December 2019.
- Parlock, Joe (9 December 2019). "The Valve Index VR Headset Sells Out Before Christmas Thanks To 'Half-Life: Alyx'", Forbes. Retrieved 2019-12-30.
- Pournelle, Jerry (January 1989). "To the Stars". BYTE. p. 109.
Bourgeois, Derek (2001-11-01). "Score yourself an orchestra". The Guardian. Guardian Media Group. Retrieved 2011-05-10.
Many composers bought an Archimedes simply to have access to the program.
- "Killer app definition". PC Magazine.
- John Markoff (1993-12-08). "BUSINESS TECHNOLOGY; A Free and Simple Computer Link". New York Times.
- Brad King (2002-05-15). "The Day the Napster Died". Wired.