The stock Android Camera app and Snapseed are two of the the apps that I use most often. I'm not sure if I just overlooked these little features or if they were added recently, but they're both incredibly useful.
Exposure Compensation in the Android Camera
Perhaps I've been using Manual Camera so often that I didn't notice this, but tapping the screen to focus brings up a little exposure compensation bar on the right edge of the screen. It's a very handy little addition meaning you don't have to rely on the camera to get the exposure level correct. This will probably see me now using the standard camera a lot more often.
Painting with the Snapseed Healing Tool
Like the newer versions of Adobe Lightroom (desktop version), you don't have to be limited to just a spot correction in the Healing tool in Snapseed. You can paint along the shape of any object you want to remove or correct. It won't always do the the job you want but I found it to be pretty good, and you can always give it a few tries (undo and redo buttons at the bottom of the screen) if it doesn't get it quite right first time.