Innovation by User Communities: Learning from Open-Source Software, by Eric Von Hippel

When people say that software is "free" or "open source," they mean that a user may obtain a copy at no cost and
then legally study its source code, modify it and distribute it to others — also for free. A software author uses his
or her own copyright to guarantee those rights to all users by affixing to the code a standard licensing notice,
such as the General Public License (GPL), commonly referred to as "copyleft" (a play on the word "copyright").
Well-known examples of open-source software are the GNU/Linux computer operating system, Perl programming
language and Internet e-mail engine sendmail. The practice of granting extensive rights to users
through licensing dates back to the free-software movement that Richard Stallman launched in the early 1980s.
Stallman founded the Free Software Foundation to counter the trend toward proprietary development of
software packages and release of software without source code. Then, in 1998. several prominent computer
hackers, including Bruce Perens and Eric Raymond,launched the Open Source Initiative. The founders had
some political differences with the free-software movement, but agreed in general with its licensing practices.
They also advanced new ideas about how to spread thepractices more broadly" (84)