There's an implied license (of sorts) in the Github ToS: We claim no intellectual property rights over the material you provide to the Service. Your profile an

There's an implied license (of sorts) in the Github ToS: We claim no intellectual property rights over the material you provide to the Service. Your profile and materials uploaded remain yours. However, by setting your pages to be viewed publicly, you agree to allow others to view your Content. By setting your repositories to be viewed publicly, you agree to allow others to view and fork your repositories. I'd assume that forking involves modifications and use, but that's not something I'd want to bet on without a lawyer.