From the "still not old enough to drink" files:

On October 5th 1991, Linus Torvalds posted his now infamous first announcement of a new operating system called Linux.

Seventeen years later, Linux is front and center as a leading operating system, displacing big Iron UNIX and making inroads against Microsoft Windows (which in 1991 wasn't an issue, though with Windows 3.1 release in 1992 it became one...).

How does a small effort started by one man, end up growing into a multi-billion dollar ecosystem with thousands of developers globally? Lots of reasons, but fundamentally it all comes down to two things as far as I'm concerned.

1) Open Source - which at the time was only Free Software. The GPL license enabled and encouraged contribution in a way that would not have been possible with other licenses.
2) A need to replace UNIX with something else.

In his original message 17 years ago, Torvalds himself provided a very simple explanation of why Linux was coming into being:

I can (well, almost) hear you asking yourselves "why?".  Hurd will be out in a year (or two, or next month, who knows), and I've already got minix.  This is a program for hackers by a hacker.  I've enjouyed doing it, and somebody might enjoy looking at it and even modifying it for their own needs.  It is still small enough to understand, use and modify, and I'm looking forward to any comments you might have.

Happy 17th Linux! It will be interesting to see what the next 17 years will bring.