Gimp

Gimp GIMP is the definitive GNU image manipulation software, ideal for tasks such as photo retouching, image composition and image authoring. It works across most operating systems and is delivered in a variety of different languages.
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Paint.NET

Paint.NET is free image and photo editing software for Windows operating systems. It’s many features include features an intuitive user interface with support for layers, unlimited undo, special effects, and a wide variety of useful and powerful tools.
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Hugin - Panorama Photo Stitcher

Hugin Hugin is an easy to use cross-platform panoramic imaging tool. You can assemble a mosaic of photographs into an immersive panorama image, stitch any series of overlapping pictures and much more.
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Zscreen

Zscreen ZScreen is a screen capture program that allows for region, window and full-screen screenshots. It can FTP screenshots and put the URL in your clipboard in a single keystroke.
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Vector Graphics

Inkscape

Inskscape is a great vector graphics editor, with capabilities similar to Illustrator, CorelDraw, or Xara X, using the W3C standard Scalable Vector Graphics (SVG) file format.
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3D Modeling

Blender

Blender Blender is a solid and respected 3D content creation suite, available for all major operating systems and distributed under GPL licensing. Create models, shade, animate and make interactive 3D.
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Crystal Space

Blender Crystal Space is a free cross-platform software development kit for realtime 3D graphics and in particular games. Officially supports Linux, OSX and Windows.
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Art of Illusion

Art of Illusion is a free, open source 3D modelling and rendering studio. It is written entirely in Java, and should be usable on any Java Virtual Machine.
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OpenFX

OpenFX OpenFX is an Open-Source 3D modeling, animation and rendering suite created by Dr. Stuart Ferguson. Its powerful feature-set includes a full renderer and raytrace engine, NURBS support, kinematics-based animation, morphing, and an extensive plugin API.
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