Apples developer site. You need to join up if you want to deploy to iOS devices! Also contains a wealth of tools and resources.
Open source 2d app development framework. Definitely worth looking at as a start for mobile app development
The platform you want to use to develop 3d applications. These can then be deployed to desktop or mobile.
virtual reality for the mobile! It really is better than you'd think. We've just started developing for this too, watch this space!