Link: http://www.gimp.org

Author: The GIMP Team

Supported Platforms: XP - Vista - OS X - Linux

Description: GIMP is a great graphics manipulation program. It is equipped with a very useful customizable interface, that even allows you to edit your pictures in fullscreen mode! GIMP also features a variety of photo enhancement options that are able to fix a number of problems caused by your lens, such as perspective distortion and vignetting.

GIMP also has a very unique feature; it allows you to bind commands to several devices, such as USB and MIDI controllers, which speed up the work a lot! It is capable of saving images in common file names, such as GIF and JPEG, and if you download some extensions, you can save your images in rare formats. There is also an option to automatically compress your images without any extra steps needed. Finally, there is an option to directly load files from remote locations using protocols, e.g. FTP/HTTP.

Paint.NET

Link: http://www.getpaint.net

Author: Rick Brewster

Supported Platforms: XP SP2 - Vista

Description: Paint.NET features an easy-to-learn and intuitive user interface. Skipping from one image to another is also made faster since the images have a small preview instead of a text description. Layers are also provided, a feature that is often found in expensive graphic editing programs. You can also download loads of tutorials and plugins from the community and forums. Paint.NET also has an update every 4 to 6 weeks, introducing new features and bugfixes. Many special effects are available, such as blurring, sharpening, red-eye removal, distortion, noise and embossing. There are also some powerful tools, for example a lot of drawing tools, a magic wand, the clone stamp, a recolor tool and a gradient tool. You are also equipped with an unlimited history, and the source code is free-to-download.

HugIn

Link: http://hugin.sourceforge.net/

Author: Pablo d'Angelo

Supported Platforms: Windows - Mac OS X - Linux - Unix

Description: HugIn is an easy-to-use panorama photo stitcher. Its main feature is that it allows you to assemble multiple photos into one picture, by pasting, tilting, stitching and overlapping them. It is based on panorama tools.

ZScreen

Link: http://www.brandonz.net/projects/zscreen/index.html

Author: BrandonZ

Supported Platforms: Windows

Description: ZScreen is a screen capture program that allows you to take region/window/fullscreen screenshots. The program is able to automatically place the screenshots on the web using FTP. You are then able to copy the URL so you can easily show the image to your friends using an IM service. Easy configuration makes sure you only have to use two keys. Once you've configured the program you can also access everything by right-clicking.

InkScape

Link: http://inkscape.org/

Author: SourceForge

Supported Platforms: Windows - Mac OS X - Linux - Fedora - Source Tarball

Description: InkScape is a vector based graphics editor program with features similar to CorelDraw and Illustrator using the W3C standard Scalable Vector Graphics (SVG) file format. It includes many SVG features such as alpha blending, markers and clones. You have access to a very streamlined interface.

CYCAS CAD

Link: http://www.cycas.de

Author: Verlag A.C.Frese

Supported Platforms: XP - Linux

Description: CYCAS is an architectural program that enables you to draw and design in two or three dimensions. It is bases on line graphics. It is also equipped with some special tools and techniques for architectural designing. There is also an intuitive interface.

Blender

Link: http://www.blender.org

Author: Blender Foundation

Supported Platforms: XP - Vista - Mac OS X - Linux - etc.

Description: Blender is a free open source 3D content creation suite. Huge amount of tools and features!!! Some examples: Revolutionary interface, 3D modelling, rigging, rendering, 3D animation (!), unwrapping, shading, physics and particles (!), realtime 3D game creation (!), huge file support and lots, huge lots of more. This programs seems too good to be true.

Crystal Space

Link: http://www.crystalspace3d.com

Author: Crystal Space Team

Supported Platforms: Windows - Mac OS X - Linux

Description: Crystal Space is a free cross-platform software development kit for realtime 3D graphics, in particular games. It is equipped with many tools and features, for example skeletal animation, dynamic shadows, haze effects, shaders, terrain with foliage and decals. Foliage is a very useful tool that enables you to randomly place objects such as trees, plants and rocks on your created terrain.

Art of Illusion

Link: http://www.artofillusion.org

Author: Peter Eastman

Supported Platforms: Windows - Mac OS X - Linux - Unix - Etc.

Description: Art of Illusion is a free, open source 3D modelling and rendering studio. It is written entirely in Java.

OpenFX

Link: http://www.openfx.org

Author: Stuart Ferguson

Supported Platforms: XP - NT - 2000
Description: OpenFX is an Open-Source 3D modeling, animation and rendering suite. It features a full renderer and raytrace engine, NURBS support, kinematics-based animation, morphing, and an extensive plugin API.

You should certainly try downloading GIMP, Blender and Crystal Space. Happy designing!