Urban Painter is a nice drawing application that allows you to create symmetrical images very easily. The program includes several reflections to make (circular or linear) and you can use different brush sizes. You can also fill the image with any color from the extensive palette. Moreover, you can invert colors, use black and white, or grayscale. If you need to correct something, there is an undo option or you can clear the whole drawing to start all over again.
Unfortunately, the application doesn't include many editing options apart from the ones described before. There are three effects to add to your drawing (circle, draw polygon, draw star), but I couldn't make them work. It would be great if you could add your own images or if it also included presets to paint. The user interface is very simple and easy to use, so anyone can use it.
In short, if you are looking for a simple application to create symmetrical drawings, Urban Painter may work for you, but it doesn't include many options.