Liquid Rescale - It is a free, open source frontend to the Liquid Rescale Library, which provides an implementation of the Seam Carving algorithm
iResizer - iResizer content aware image resizing software rescale photos without rescaling the subject.
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.