Google Cardboard SDK
https://developers.google.com/vr/unity/download
Oculus
https://developer3.oculus.com/downloads/game-engines/1.10.0/Oculus_Utilities_for_Unity_5/
Sample VR Assets
https://www.assetstore.unity3d.com/en/#!/content/51519
https://plarium.com/en/blog/vr-tech-future-of-virtual-reality/
https://plarium.com/en/blog/smartphone-tech-impacts-mobile-gaming/