The "Blank Canvas" Specialists
Starting from a blank canvas, these Apps enable the artist to draw or paint directly in various media. They usually do only one thing, but do it very well. They also tend to be a lot of entertaining fun. There are some traditional media simulators that do a remarkable job, and a number of not-so-traditional approaches that only a computer could produce. Here are some of my favorites.
Camera Apps - the Other Way to Get Started
One of the most exciting developments is the ability of digital cameras and their apps to show the effects of various filters and distortions as you take the picture. This is tremendously helpful in framing your compositions, and in getting the right feel for the picture.
Mostly I use my phone camera for photography, it's easier to handle and is more likely to be with me. There are, however, a few that work only with one or the other.
Some Very Useful Graphic Apps
Nancy Freeman has a decades-long fascination with digital art which she supports by painting portraits and teaching various art subjects. Right now she devotes most of her creative time to digital art because it's so satisfying.