I co-founded an open source startup six years ago (based on a project that I also co-founded), and probably have a book or two in me on the subject. In short,

I co-founded an open source startup six years ago (based on a project that I also co-founded), and probably have a book or two in me on the subject. In short, building around a third-party open source project is probably an easier win than building around a project that you founded and maintain. (Forking, on the other hand, is not something I'd recommend.) While not required, it's a really good idea to make friends with the community organizers and, ideally, find some way to contribute both code and funds upstream when you become successful - after all, your business is based on their continued existence. That said, although it's certainly much harder to succeed under these terms, maintaining your own project is a valuable, rewarding experience, and gives you significantly more control over its direction. Just remember that open source code has an accounting value of 0 - so any open source IP you create is not capturing value in the company, and unless you're careful, one-to-one professional services don't either. You'll have to figure out how to make your company valuable with valueless code another way. (Hosted services are a good example.)