The father of the movement Richard Stallman, founded the FSF in 1984 and from this cause Open Source was born. Open Source Software (OSS) and the FSF movements are different but are not unlike two political parties in the development community. The OSS was founded, in 1998, specifically to temper or modify these idealistic philosophies of the Free Software movement. See http://www.gnu.org/philosophy/free-software-for-freedom.html for more explanation of the difference between the two movements.
The basic philosophy behind open source is very simple: When programmers can read, redistribute, and modify the source code for a piece of software, the software evolves. People improve it, people adapt it, and people fix the bugs. And this can happen at a speed that, if one is used to the slow pace of conventional software development, seems astonishing.
There are many active Open Source Software projects but some may be thinking you get what you pay for, so if it's free there must be something wrong with it. Sometimes this is true but there are open source software projects providing stable, scalable applications. The key is to know where to look and what to look for when evaluating the stability and scalability.
Here are a few interesting facts and examples of Open Source projects:
Apache is the number one web server at nearly 62% of all installations. Second place was help by Microsoft at just under 27%. (Source: Netcraft)
GNU/Linux is the number two operating system at nearly 30% of all servers behind Microsoft operating system at nearly 50%. (Source: Netcraft)
Sendmail (a mail transport agent) sendmail has become one of the standards of the Internet's infrastructure (TCP/IP, Apache, sendmail).
BIND the Berkley Internet Naming Daemon responsible for mapping domain names to IP addresses ran on 95% of all public reverse DNS servers. (Source: Information Sciences Institute of the University of Southern California).
MySQL founded in 1995 by two open source veterans, Michael "Monty" Widenius and David Axmark, with the help of Allan Larsson and claims 4 million installations worldwide and 30,000 downloads of the software per day making MySQL by far the planet's most widely distributed open-source database. (Source: mySQL)
PHP is a widely used general-purpose scripting language that is especially suited for Web development and can be embedded into HTML and as of May 2003 it was being used on 12,487,030 domains and 1,321,203 IP addresses. (Source: PHP)
Linux Operating System is over three years old and has grabbed 13.7 percent of the $50.9 billion market for server computers, and that figure is expected to jump to 25.2 percent in 2006, putting Linux in the No. 2 position. (Source: IDC)
SourceForge a site providing support tools and resources for the OSS/Free Software movement recently announced a major two year milestone of having more than a half million registered users, as well as a site record of nearly 63,000 registered projects. This is amazing growth of 25,000 new users per month.