Google Cardboard is an affordable, immersive, and customizable virtual reality hardware component. The Android SDK enables developers to construct VR apps for Android from scratch, convert existing apps into VR, and provide a method for turning on and off 3D simulations. The SDK also provides stereo sound rendering and head tracking capabilities.
Google and Lenovo released the first Project Tango handset this week at CES. The phone includes an array of sensors that let apps cover real-world objects with digital overlays. It's sort of like augmented reality on steroids. Project Tango needs apps, and Google us willing to pay.