The free Unix workalike created by Linus Torvalds and
friends starting about 1991. Tthe pronunciation /lee'nuhks/ is
preferred because the name `Linus' has an /ee/ sound in Swedish
(Linus's family is part of Finland's 6% ethnic-Swedish minority).
This may be the most remarkable hacker project in history -- an
entire clone of Unix for 386, 486 and Pentium micros, distributed
for free with sources over the net (ports to Alpha and Sparc and
many other machines are also in use).
Linux is what GNU aimed to be, and it relies on the GNU toolset.
But the Free Software Foundation didn't produce the kernel to go with
that toolset until 1999, which was too late. Other, similar efforts
like FreeBSD and NetBSD have been technically successful but never
caught fire the way Linux has; as this is written in 1999, Linux is
seriously challenging Microsoft's OS dominance.
An earlier version of this entry opined "The secret of Linux's
success seems to be that Linus worked much harder early on to keep
the development process open and recruit other hackers, creating a
snowball effect." Truer than we knew. See bazaar.
(Some people object that the name `Linux' should be used to
refer only to the kernel, not the entire operating system. This
claim is a proxy for an underlying territorial dispute; people who
insist on the term `GNU/Linux' want the the FSF to get most
of the credit for Linux because RMS and friends wrote many of its
user-level tools. Neither this theory nor the term `GNU/Linux'
has gained more than minority acceptance).