Pixie is an open source RenderMan renderer for generating photorealistic images. You can compile Pixie on Windows (using Visual Studio 2005), Linux and on OSX (using XCode or unix style configure script).

Toxic is a physically correct global illumination renderer aiming to produce photorealistic images and animations.

Sunflow is an open source rendering system for photo-realistic image synthesis. It is written in Java and built around a flexible ray tracing core and an extensible object-oriented.

WinOSi is an Open Source, freeware rendering tool for creating real photo-realistic images.

Dia is a program to draw diagrams. Like GIMP can be used as an Open Source replacement for Photoshop, Dia can serve an an Open Source alternative to Visio.

AutoTrace is a program for converting bitmap to vector graphics.
The aim of the AutoTrace project is the development of a freely available application with a functionality similar to CorelTrace or Adobe Streamline. I hope that it will become better than all commercially available programs. In some aspects it is already better.
AutoTrace is free software. AutoTrace is distributed under the term of GNU GPL.

OpenFX is an Open-Source 3D modeling, animation and rendering suite created by Dr. Stuart Ferguson. He made the decision to release the source code to the public in the middle of 1999, and the product formerly named SoftF/X was renamed to OpenFX. It has now been released under the terms of the GNU General Public Licence.

Imgv is a unique and feature rich Image Viewer. It is released as free software with full source code. Imgv is portable and can run on Windows, Linux, BSD, OSX, and other operating systems.
Features include a GUI that doesn't get in the way of viewing your images, a file browser, slideshows, zooming, rotating, on-the-fly Exif viewing, histograms, fullscreen support, wallpaper setting, the ability to view 4 images on the screen at once, adjustable thumbnail sizes, playlists, view and download images from Web sites, movie playing, file searching/filtering, multiple directory loading, transitional effects, image hiding and more.

Wings 3D is a subdivision modeler. It is possible to assign materials, vertex color, UV coordinates and textures.

The Irrlicht Engine is an open source high performance realtime 3D engine written and usable in C++ and also available for .NET languages. It is completely cross-platform, using D3D, OpenGL and its own software renderer, and has all of the state-of-the-art features which can be found in commercial 3d engines.