Modern life is stressful but coloring has become a trendy new way to combat stress with a host of books available for adults to colour in as a form of meditation and mindfulness. Abstract Coloring Book is a free app for doing the very same thing providing complex black and white images for you to colour digitally by tapping the screen. This app has a huge set of images from mandalas to birds flowers and abstract sketches. You can zoom in to fill the tiny spaces and there's a neat colour tray to pick from. Simple and smart.