I think version control is a good analogy (Subversion and Git). It enables whole classes of products and services to be built on top of it, but that only happen

I think version control is a good analogy (Subversion and Git). It enables whole classes of products and services to be built on top of it, but that only happens because the basic tool is unambigiously free and can be used everywhere. Trying to monetize the basic thing just damages what makes it valuable.