Tux Paint - Tux Paint is a free, award-winning drawing program for children ages 3 to 12 (for example, preschool and K-6).
Kid Pix - Kid Pix is a bitmap drawing program aimed at children.
Lil' Picasso - Lil Picasso is a coloring and creativity package for children.
Disney Coloring World - Create, color and paint hundreds of your favorite Disney characters using powerful, easy-to-use creative tools.
childsplay - Childsplay is a collection of educational activities for young children and runs on Windows, OSX, and Linux. Childsplay can be used at home, kindergartens and pre-schools.
Hexonomy - The world's largest ever work of art.