The two Google smartphones were released two years ago and it seems that since then the company forgot about them. The devices did not receive the Zero Shutter Lag feature for the cameras, despite packing the required hardware. Pixel and Pixel XL did receive the feature and it seemed that Google decided to keep it only for Pixel smartphones. The Nexus community released an unofficial camera app soon enough and they called it Google Camera NX. The app contained all the features used from the Pixel devices.
The Zero Shutter feature is important
This feature mixes problems using HDR+, allowing users to take pictures in rapid succession. This is perfect for the fast objects are the subject of a photo shoot.
If so far the Google Camera NX mod managed to keep the balance between Nexus and Pixel lines, once the Pixel 2 device was released, more and more features have been added to the modified camera app.
Google Camera 5.1
The most recent update for Nexus phones is based off the official Google Camera 5.1 app and it includes Motion Photos and Face Retouching features. The latter is a beauty mode feature which smooth out imperfections and makes users look better, especially for selfies. Motion Photos uses sensor motion in viewfinder and takes a few seconds of video on each side.
The one in charge of developing the camera app, XDA Senior Member, Charles_I, uploaded two versions: one with Zero Shutter Lag and one without. The version without non-Zero Shutter Lag is almost identical to the official Google Camera app used on the Nexus 5X and 6P and it also adds the Motion Photo feature.
The Zero Shutter Lag version behaves similarly as the official app on first-gen Pixel phones.