This is a fast sketch that i have done testing Krita. http://krita.org/
This is the forum . http://forum.kde.org/viewforum.php?f=136
Krita is a KDE program for sketching and painting, offering an end--to--end solution for creating digital painting files from scratch by masters.
Fields of painting that Krita explicitly supports are concept art, creation of comics and textures for rendering.