In case you missed it, Google just released an official Camera app into the Play Store. It isn't exclusive to Nexus or Google Play devices either, so go ahead and download it. I'll wait.
Alright, let's dive into the app's new Lens Blur feature. Google's released a blog post with some of the details. In short, it's one of the features of HTC One M8's duo camera made available to any Android device running Android 4.4.