From “Andreessen singles out consumers as key to Web future“, in InfoWorld (26 May 1999):
[Mark Andreessen] then switched gears and talked about the “serial killer apps” on the Internet. A serial killer app, as opposed to a killer app, just keeps getting more useful and more killer as people keep coming online, according to Andreessen.
Andreessen listed the five serial killer apps as: e-mail, the Web, instant messaging, online calendaring, and auctions. …
Andreessen said serial killer apps are the reasons people get online, but once online they are not limited to these five arenas.