Hurray! GitHub just announced yesterday that all of the core features are now free.
Private Repositories Are Free for Teams
What this GitHub Free plan means now is that small teams can also enjoy private repositories – meaning my Unix Tutorial @ GitHub and similar teams can both contribute to open source and also keep some work-in-progress efforts or internal projects private without immediately having to pay.
Particularly relevant is the fact that many services (GitHub as well) offer some paid features only for team plans, and expect teams to be 3 people or more.
Unlimited Collaborators for Private Repos
This is another great improvement – previously only paid teams allowed unlimited contributors for private repositories. Now this limitation is gone.