The thing is, if an open source software becomes really important to many companies, they start donating millions of dollars to the foundation maintaining the project.

A lot of these companies are also part of a committee that decides how to progress the software.

In some cases, some companies create a software but then release it in public so that others can also contribute along with their own dedicated team.

Happens at ThoughtWorks for projects like Selenium. AngularJS has commits from Teams from Google, Microsoft and Adobe and some small independent contributions.

There are times, when an individual starts out with something as an open source pet project in their leisure time. An example is LightTable IDE by Chris Granger or for that matter Django REST Framework for making REST APIs which runs on top of Django Web Framework.

In such cases, The founders went for crowd sourced funding and raised thousands of dollars stating that they would give their full time to the project and quit their day job to focus on it completely.

Also there are scenarios where companies providing you day job become interested in your work and start paying you for dedicatedly working on it because they run their business around that — Happened at Joyent, the cloud services provider company that where Ryan Dahl, the creator of NodeJs worked. At Google it’s quite common for side projects becoming major open source work for the company.

The thing is if you start out to make a difference and you can prove that you can do it, there are enough people who would like to help you in achieving it.