In October of 1991, Linus Torvalds, a 21-year-old computer-science student at the University of Helsinki, made available on the Internet a kernel of a computer operating system he had written. Called Linux, it was a rudimentary version of the ubiquitous UNIX operating system, which for more than a decade had been a mainstay of corporate and academic computing. Torvalds encouraged other programmers to download his software—for free—and use it, test it, and modify it as they saw fit. A few took him up on the offer. They fixed bugs, tinkered with the original code, and added new features, and they too posted their work on the Internet.

A version of this article appeared in the September–October 1998 issue of Harvard Business Review.