GIMP - GIMP is a multiplatform photo manipulation tool.
IcoFX - IcoFX is an all-in-one solution for icon creation, extraction and editing.
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.
RealWorld Icon Editor - Create Windows icons and Mac OS icons from images and 3D models in an integrated icon maker.
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
IconLover - Icon editor for Windows.