Anyone can make their own Cardboard viewer with the open designs ready for download.
If you'd rather not DIY, you can choose from a family of certified viewers, including the Mattel View-Master and Zeiss VR One GX, on sale now.
The Cardboard SDKs for Android and Unity have been updated to address two requests: drift correction and Unity performance. This update includes an overhaul of the sensor fusion algorithms that integrate the signals from the gyroscope and accelerometer. These improvements decrease drift, especially on phones with lower-quality sensors. The Cardboard SDK for Unity now supports a fully Unity-native distortion pass. This improves performance by avoiding all major plugin overhead, and enables Cardboard apps to work with Metal rendering on iOS and multi-threaded rendering on Android.
Finally, you can now explore Google Street View in Cardboard.