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.
IconWorkshop - Application to create and manage software icons. A must for developers.
MyPaint - MyPaint is a fast, distraction-free, and easy painting tool for digital artists.
IconLover - Icon editor for Windows.