Open Source History
It’s a complex question. The best material to find the answer you want is “Eric S. Raymond: A Brief History of Hackerdom”. Thanks to fellow Edgeryder perulera who pointed that jewel piece of text out once.
Open source has basically existed as long as programming has existed, but the tools for collaboration have evolved a lot of course, esp. with the advent of the Internet.
The closest thing to a key moment in that (rather short) part of open source history that I lived through personally was when sourceforge.net opened in Nov 1999 [source]. They offered all kinds of open source project hosting and collaboration tools for free, and with that, founding an open source project became ridiculously easy and cheap. And the number of projects exploded …