I developed simple VR set with Google cardboard SDK and Unity 3D. It is a Jump Program that after the movie 'Matrix', and I tried to implement motion detection and auto-walk function. I had have to understand even little about Quaternion and Euler angles. Although it was not a perfect result, I could have implemented cannon jump action in the VR scene which is triggered by real jump in the real world. Also, walk autonomously in the VR world doesn't need any external input devices. The related scripts are down below.
I am also interested in game development. So, I made a simple shooting game by Unity engine. Getting to know game development was a totally new thing, but like other new challenges in life, it was really great and fun experience.