This one is called MyBrushes and it is a painting app. What makes it different is the ease of use compared with other apps designed for adults.
You can find my screencast of it here.
It has a lot of brush styles that you can easily manipulate to your own taste. There is a cute animated preview of the brush you choose too.
The canvas is huge and the controls clear. Even a novice could learn how to use this app very easily. It exports to PNG format and can import photos for you to work on.
There is even a whole list of effects that can be applied to them.
EDIT - This app works with Wacom tablets and key shortcuts too.
The software is packed with features. It will import pretty much any format of image you are likely to have and supports layers, so this is great for novices and more experienced graphic artists.
Here is a little doodle I did in all of about 5 minutes.
What I will make clear, is that this is a FREEHAND PAINTING app, not one that has pre designed shapes for you to fill. It does what it does really well.
MyBrushes also has a playback feature, you can record your art being made! Fun to do and great if you are trying to teach art classes or demonstrate.
For those with an iPad, the same people make an app for that, called MyBrushes Pro. Very much the same with a couple of tweaks. The advantage of that is that it supports 4 different brands of pressure sensitive stylus - to date - the Wacom Creative, Pogo Connect, the Jaja Hex3 and the Adonit Jot Touch, to give you the ultimate digital painting experience.
Here is the link to the web page for more details. I believe there is a free trial to be had, so you can see for yourself what great pieces of software these are.