I want to do a mobile version of an old game I used to like called Bow And Arrow (video, game). There's a project already port it in Ruby. I'm wondering if I can do a remake of this game. Do I have to get permission from the creator, or does it only matter if I use the same resources (graphics and sound)?
Generally, and nearly universally around the world: game systems (pure mathematical formulas and algorithms) can't be copyrighted, and thus can be copied freely, even without being nice and asking. However, In some jurisdictions they can be protected - in parts or whole - by patents.
For everything else, ask a lawyer.