Advantages of Open Source
The first big difference betweeen open and closed source is "openness". Open source software is open to analysis and improvement by the end user. Another big difference is cost; open Source software is free, by definition. Free to download, free to use, free to give away. It should run on the widest possible range of hardware and be useful to the largest number of people.
With this mentality, users of Open Source Software become contributors, whether they contribute direct work-hours or general concepts. Feedback is direct, and the development of the software follows the opinions of its users more closely than with any other model.
Open Source Software is an Option for Everyone
There are a lot of common misconceptions about Open Source Software (OSS). Most people have grown accustomed to the two major operating systems - Windows and Mac OS X. The important thing to know about these two is that they are both ‘closed source’ options.
Neither allows modification of the operating system, or distributes the code that comprises it. Apple takes it one step further and locks OS X to their own proprietary hardware. This is completely opposite the philosophy of OSS.
Most Open Source Software has been around as long as its Closed Source counterparts and received just as much development time, often from people who are truly impassioned about their work.
For-profit software developers may have a vested interest in keeping their software on one platform, and documents may need to be converted or mangled to go between users. OpenOffice.org is considered by many to be as full-featured as Microsoft Office, but while Microsoft Office is only available on Windows and Mac OS X, OpenOffice.org is available on both, in addition to every flavor of BSD, Linux, Solaris, and more.
It's About Community
The concept driving Open Source is community development -- the idea that no matter who you are, or what you do, there are people like you, doing what you do, and doing it with Open Source.
Large companies may be deaf to the needs or concerns of their users and customers. Feuds between software empires may create software incompatibilities in otherwise compatible systems.
This is not the case with Open Source Software, where the community is self-sustaining, and anyone may contribute a change or fix a problem.
You May Be Using It Already
The Open Source mentality is more popular than most people realize. Mozilla Firefox is an Open Source web browser that sees 30% worldwide usage, and is compliant with more standards than Microsoft Internet Explorer. Wikipedia, the free encyclopedia based on the Open Source MediaWiki software, is one of the most visited websites in the world, and has no advertisements or other for-profit interests. The entire website is community-driven, and all content is free to read and amend.
For Your Business
Cost comparisons over 5 years show that companies who use Open Source software save money based on more than just initial cost. Support tends to be much cheaper, and is available from more sources than commercial alternatives. For more information, please refer to this White Paper: IT Cost Optimization Through Open Source
Open Source Families
Linux is a popular Open Source operating system developed originally to be similar to UNIX, but free to download and modify. There are countless different distributions of Linux, and it is being used in nearly every conceivable application.
BSD (Berkeley Software Distribution), is derived from the UNIX operating system, and has been under development in one form or another since 1977. It is significant not only as a progenitor of UNIX-like operating systems in general, but also of the BSD Software license. This license has been used to distribute all manner of free, Open Source Software to this day.