The human hand can do it without any trick or help. And don't let anyone tell you a green apple is easier to break than a red one. Colour doesn't matter. You just need to practise. Start with an apple that is easy to break like a golden delicious (green). Then work yourself up the chain until you manage to break a granny smith (also green). If it is too hard for you, use your leg to support your hands.
The attached vid or the pics show you exactly how to do it.
Maybe you ask yourself why people break their apples apart....
1) It's way cool
2) It's even cooler when someone sees you break one apart as if it is the most natural thing in the world
3) you will instantly see if the core is okay.
4) if the seeds are not existent or if they are way to small or if they look unhealthy, think about pesticides and bury that poor thing.