GIMP is the GNU Image Manipulation Program for photo retouching, image composition and image authoring.. (free software replacement for Adobe Photoshop).
GIMPshop was designed to specifically ease the transition for Photoshop users.
Inkscape is a Vector Graphics Editor, similar to Adobe Illustrator, that strives to be SVG Compliant, open source, responsive and extensible.
Blender 3D is the open source, cross platform suite of tools for 3D creation..