I noticed that there is no thread about AzDrawing or AzPainter so I here it is.
These are two free japanese programs for inking and painting. The AzDrawing has official english version while AzPainter2 was translated by some fans. I use a lot of the first one at work for inking cartoony stuff with smooth lines. It works fast, has nice comfortable curve tool, allows for rotating the canvas and you can save in PSD format. AzDrawing has also simple animation mode where you have onion skin feature and layers are used as frames.
I haven't used AzPainter2 as much. It has mostly basic round brushes like openCanvas but you can give brush tip some texture to make more interesting marks. Also there is Waterbrush which gives a nice color blending effect. Other features are layers with different blending modes and preserve transparency like in Photoshop or Gimp, basic adjustments in menu like Levels, Brightness/Contrast and filters. Great thing is that filters are limited to those that are actually the most helpful (at least I use them in Photoshop) like Unsharp mask, Gaussian blur, Polar coordinates. For technical or perspective stuff you also got different snapping modes - Linear, Radial, Concentrical and Elliptical.
Official program page: http://hp.vector.co.jp/authors/VA033...azdrawing.html
Direct link to english version: http://hp.vector.co.jp/authors/VA033...draw113_en.zip
Official program page: http://hp.vector.co.jp/authors/VA033...zpainter2.html
Download to translated english version http://www.mediafire.com/?rdmjiy53u0k
Have fun .
EDIT: HERE there is AzDrawing (azdw2beta.zip) with improved interface and new features but in beta version.