http://techcrunch.com/2014/12/10/google-updates-its-cardboard-vr-app-launches-sdks-for-android-and-unity/ 

" the big surprise of this year’s Google I/O, and Google today announced that more than 500,000 of these extremely minimalist, phone-based virtual reality viewers have shipped since then. The early cardboard app was a lot of fun, but over the last few months, it felt like development had stalled a bit. Today, however, the company is launching an update to the cardboard app and new SDKs. It’s also showcasing some of the apps that developers have created over the last few months."