http://mypaint.intilinux.com/
MyPaint is an application for digital painting. It supports pressure sensitive graphics tablets. Has many options for the creation and configuration of brushes. The canvas is unlimited, so it is not resized. It has basic support for layers.
PLATFORMS: Windows, Linux
LICENSE: GPL
PRICE: Free
http://code.google.com/p/gps-gimp-paint-studio/downloads/list
http://ramonmirandavisualart.blogspot.com/2009/02/gps-v10.html
Gimp Paint Studio is a suite of tools to add it to Gimp especially to draw and paint. It has lots of different brushes, and also proposes a function of loading preajustaments. It was developed by the Spanish illustrator Ramón Miranda.
PLATFORM: Multiplatform
Code License: Artistic License / GPL
CONTENT LICENSE: Creative Commons BY-SA 3.0
PRICE: Free