If you love painting and great freeware, there are many programs available on download sites such as snapfiles.com and download.com.
For the Corel Painter crowd, Dogwaffle is a great alternative. It has a freeware version and several levels of pay versions, which allow advanced brush creation and editing and special 'particle' brushes which can create organic-looking branches and roots, somewhat like the tube-brushes in Painter.
In the freeware version, the tools are basic but still very useful. You can create them using graphics files(as demonstrated in some of the 'organic effects' brushes) or using the 'custom brush' tool which allows you to manipulate the size and number of 'bristles' in the brush. Other brush types that can be created are the pastels, which are used with the paper texture feature. This feature can create pastel paper, canvas, watercolour paper, and other realistic or non-realistic patterns which resemble real paper while you paint.
The watercolour brushes in the free version are simple brushes, some with texture and some without, that bleed and blend with other colours for a realistic effect. The oils and tempera are similar to the watercolours, but less transparent. The commercial versions have more options for these brushes as well, including the thick(impasto) oils, dropshadows, and translucent and opaque watercolours. Dogwaffle even allows some animation, and even onionskins for animation cells in some versions.
Project Dogwaffle can be downloaded for free or bought for as low as $29 at this website:
TheBest3D.
