Google Camera (free - no IAP) is a nice replacement for the stock camera app that comes with most Android devices. Developed for phones and tablets running at least Android 4.4+ KitKat, Google Camera has many of the same features that should be expected from other high end camera apps.
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Pro HDR mode
HDR can be activated or deactivated with one swipe of the thumb.
Pro Lens Blur
A recently added feature to Google Camera, Lens Blur gives you the SLR like function of creating images with shallow depth of field, or limited areas of focus. Basically, lens blur will only blur the background in order to put more emphasis on an object.
Pro Simple clean interface
Google Camera has a very easy to use and simple interface, with the most important controls right at your fingertips. Google has redesigned the Camera app for every skill level of user, making photography more accessible to everyone.
Pro Photo Sphere
Use Photo Sphere and Google Camera to create three hundred and sixty degree panoramic photos easily. Photo Sphere photo images allow the viewer to move around within the world you have created, move up, down, left or right to see everything. Photo Sphere also gives you the tools to create your own Google Maps street view and share it with other Maps users.
Pro It is free
It's free if you have one of the supporting devices (Google Nexus or Pixel).
Pro Support panorama shots
Which is also supported by the Android stock camera.
Con Requires Android 4.4+ (KitKat)
The Google Camera app system requirements do require Android 4.4 (KitKat) or better, as a result this does leave out a lot of older phones and tablets. The app does take advantage of features of higher end phones, so you will need to upgrade if your device has an older version of Android.
Con Limited device support - Only available for Google Nexus and Pixel
In 2016 they stop providing Google camera for non google devices. You can download APK and install. But it crashes and most likely the video camera will not work.
Con Photo Sphere does not work on all CPUs
For example, Android-Lenny 4.4 does not support this.