GitHub Free now includes unlimited private repositories. For the first time, developers can use GitHub for their private projects with up to three collaborators per repository for free. Many developers want to use private repos to apply for a job, work on a side project, or try something out in private before releasing it publicly. Starting today, those scenarios, and many more, are possible on GitHub at no cost. Public repositories are still free (of courseno changes there) and include unlimited collaborators.

Source: New year, new GitHub: Announcing unlimited free private repos and unified Enterprise offering

Finally! This is good news, following the Microsoft acquisition.