When reviews of Google’s Pixel phone came out, the camera was the highlight of the phone. In fact, it was a testament to the work Google had put in that photos from the camera were talked about in the same ballpark as the iPhone 7 and Samsung Galaxy S7. Most smartphones use the same Sony image sensor, in other words, what makes one camera better than the other is the software. The Google Pixel camera app was special, and now it works on other phones.
What you get is not an official version of the app. A Ukranian developer has ported the app so that it works on other Android phones with the Snapdragon 820/821 or 835 processors. One of the staff at XDA Developers ran the app on LG G6, a OnePlus 3, a OnePlus 3T, a OnePlus 5, and a Samsung Galaxy S8 without any issue.
What makes the Pixel Camera app special is the HDR+ image processing that produces great images in even low-light conditions. The app uses the Hexagon digital signal processor to take a continuous stream of images from the time the app opens. When you take a shot, all the app does is mark the time, and use the images to build the best possible HDR image.
Please remember that the app probably includes optimizations for the specific hardware in the Pixel and will probably not produce images as good as the Pixel.