PaintTool SAI is a lightweight software focused solely on painting and drawing. Because of that, it doesn't include some of the common features that similar software has, such as text layers, gradients and shape tools, and therefore the finalizing touch of drawings is to be made in another program. This is helped by SAI's ability to export the files to other popular formats, like .psd or .bmp, in addition to its .sai-format.
Various raster drawing tools are implemented, such as the Airbrush, Watercolor, Pen and Marker, which can all be easily customized, and stored in slots in the user interface of the application. There is also a set of vector drawing tools intended for inking, which, like the raster tools, can be configured to be pen pressure sensitive. However, the vector tools are not affected by selections, and therefore need to be adjusted by other vector tools.
Downloadable version is a 31-day trial and the full version is available for 5250JPY, which is roughly 54 USD