Other comparison would be that we are equipped with tools (software) other people build completely for free. And we can improve those tools and propose them to be implemented (PR). Or just continue using our custom-modified tool (Forking).

And we often get the luxury to ask questions and receive answers (Issues) directly from the manufacturer (author, contributor).

And we need not much investment to set up our own factory... thus "materials" can be free and then we give away our product.