Open Source Software is software that is available with source code, redistributable for free and any changes made need to be redistributable for free. A more detailed definition is available here, http://www.opensource.org/docs/definition .

If software does not meet all the Open Source criteria then it is not Open Source software. Shareware or software that is available for free like Adobe Acrobat Reader is NOT Open Source software. Adobe Acrobat (which doesn’t claim to be Open Source) breaks the cardinal rules of Open Source: it cannot be freely redistributed and the source code is not publicly available. However, merely allowing redistribution and having publicly available source code do not by themselves explain the Open Source movement’s appeal or why it’s so revolutionary.

Eric Raymond, in his essay “The Cathedral and Bazaar” (a great essay that everyone interested in Open Source should read) says that the Open Source is like a Bazaar in that there is a community, participation, energy, bartering and goods for everyone to try (free software). By contrast, most commercial software, like Adobe and Microsoft, is developed in the Cathedral. Development is done behind the firewall at a campus and not at the Bazaar; source code is protected and can only be seen by a few chosen people. If there are bugs or problems they will be found by the chosen people (hopefully) and then given back to the masses with assurances that it is fixed (but no source code to prove it).

Advantages

1) “Many eyeballs tame complexity” – I found this in “The Cathedral and the Bazaar”. If you’ve ever developed or even used software you know that bugs are software’s worst enemy. With an Open Source project you are asking a community of interested people to try the software and take a look at the source code to find bugs. One of the biggest users of this method of QA is the Firefox web browser. Firefox is an Open Sourced web browser that the community develops and QAs. When security bugs are found in Firefox a patch is created much faster than a similar security bug in MS Internet Explorer. See Reference http://news.cnet.com/Mozilla-Were-more-secure-than-Microsoft/2100-1032_3-5630529.html

2) Open Source software helps technology companies start up faster and cheaper – In the mid-to-late 90’s when the Internet was first taking off, there were not that many commercial tools that were available to create an infrastructure for technology companies. The only Database servers, web servers, development environments were created by a very few companies (think Cathedral). The software was very expensive, ran on expensive hardware and needed to be installed, configured and maintained by knowledgeable consultants. Fast forward to 2008 Open Source has made it much cheaper to start-up a technology company. Start-ups can now use entirely Open Source software to power their technology infrastructure, this group of software is know as the LAMP Stack.

L – Linux, an Open Source operating system comparable to Microsoft Windows Server
A – Apache, an Open Source server for serving web pages
M – MySQL, an Open Source relational database server
P – PHP (or Perl), an Open Source programming language

Now instead of spending money on expensive software, hardware and consultants start-up companies can now focus in on advantage #3.

3) Open Source software helps innovation – There are hundreds of useful websites that use Open Source as the basis of their services. A few of the innovative companies that have leveraged Open Source software are Facebook, Meebo, Salesforce.com, Google and the Mozilla Foundation. All of these companies have been able to use Open Source software as a starting point to develop new and exciting software and services.

Disadvantages

1) Business models are more difficult with Open Source software projects. If you are giving away software you are not making any money from selling software. If the reward of creating software is eliminated, how will developers survive?

2) Not all Open Source projects are popular and have a community. Just because a project is Open Source does not mean that it will gain a following and benefit from the advantages above. Only the best Open Source software will reap the advantages. To understand how much Open Source software is available take a look at FreshMeat or SourceForge. There are only a few Open Source projects that only have a meaningful community participating in development and QA.

3) Not all Open Source software is high quality. A great deal of Open Source software is created by part-time developers that don’t have a lot of time to maintain their software.

Caveats aside, great innovations have come from Open Source and great companies have been built using Open Source software. Overall, Open Source’s advantages outweigh the disadvantages. Because of it’s unique licensing and sharing there will be more innovation and more great companies founded.