What are some alternatives?
When comparing Artrage and PaintTool SAI, you can also consider the following products
Krita - Krita is a professional FREE and open source painting program. It is made by artists that want to seaffordable art tools for everyone. Concept art. texture and matte painters, illustrations and comics.
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
Autodesk SketchBook - SketchBook drawing and painting software provides designers, architects, and concept artists the tools to sketch ideas quickly and create beautiful illustrations.
Clip Studio Paint - Powerful drawing and illustration tool.
Adobe Photoshop - Adobe Photoshop is a webtop application for editing images and photos online.
GIMP - GIMP is a multiplatform photo manipulation tool.