Well. Paint Tool SAI is a very light, but capable application focused on art, mostly. The simplicity of the interface and the various tools make it a very good choice for beginners and experienced artists alike.

SAI has a very user-friendly interface which makes navigating through functions easy. It's like a more simplistic version of Photoshop, just without all the fancy filters or tools. It was not at all difficult for me to adapt to. I personally love the various brushes and tools. The brush tool in particular actually blends colors together automatically for you (whereas in Photoshop you have to do it manually). The tools come with many options that allows you to customize them and also create entirely new tools that can be personalized to fit your style. Custom brush shapes and textures can be downloaded for free around the internet to create even more unique tools. Also, you can save files in SAI as PSD's, which allows easy transfer to Photoshop for editing without losing the layers. Helpful if you need to go back and forth between SAI and Photoshop. Lastly the View Rotation button is a Godsend. It allows you to rotate your canvas, making it easier to create certain brushstrokes without having to constantly use the Transformation tool. Also there's a button that flips the canvas horizontally, which is helpful to view your drawing in an opposite way to catch mistakes, again, without having to "transform" it constantly and loosing the quality of the image. Overall it's a nice program for drawing. And its cheap!

intuitive stroke and smooth drawing ( sketch and coloring )