piZap - Free online photo editing software.
Krita - Krita is a professional FREE and open source painting program. It is made by artists that want to seaffordable art tools for everyone. Concept art. texture and matte painters, illustrations and comics.
FotoFlexer - FotoFlexer is the most powerful online photo editor in existence.
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
Photoshop.com - Photoshop.
GIMP - GIMP is a multiplatform photo manipulation tool.