Why is it Open Source?

Before I joined current team, I didn't have much practical experience in open source project. All the products I have worked for before are just commercial and aimed for those big customers.However, things like Linux,Firefox or eclipse have been quite popular there for a long time. Then I start wondering why they can survive there in such a commercialized society. Why is it open source?

Take eclipse as an example, I guess it should be the most popular IDE in java world. And you can download almost all the source code of eclipse. There are thousands of people who are developing the official eclipse and millions of developers who have used eclipse once or more. Then why is it open source?

From the aspect of business I can think of the following reasons so far: gain market share, set up standard, and win the reputation from programmers.

If eclipse is not open source, there won't be so many developers who indulge in creating new plug-ins for it and making use of this framework for their own purposes. You can find numerous commercial products there based on eclipse. Without the open source, it would be almost impossible for them to create their products from eclipse.

When the software gains the market share, it will have the trend of becoming kind of standard in solving similar problems. Companies who initiated the open source project will hence run ahead of their competitor as they always have to follow the "standard".

Last but now least, I guess that everyone prefers free software. No one wants to pay a hundred dollars for something if he can get another similar one for free. For me, if someone gives me free service and it is in fact very good, I will have a good feeling for him. The same thing is applied to the company who make the software open source.If it is a good software and the inventor make it public, programmers may have kind of emotional preference to this company.

Personally, I like free things. Google maps, gmail, linux, youtube (though not all of them are open source, but they don't need to be)... They are great things. If all the software needed to be developed can be open source, we will have more creations in IT industry.