PhotoFlare - Quick, simple but powerful Cross Platform image editor.
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.
showFoto - ShowFoto is the standalone image editor of the digiKam project.
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
PhotoDemon - Lightweight portable BSD licensed photo editor for Windows focused on performance and usability.
GIMP - GIMP is a multiplatform photo manipulation tool.