Graphics
Gimp
GIMP is the GNU Image Manipulation Program. It is a freely distributed piece of software for such tasks as photo retouching, image composition and image authoring. It works on many operating systems, in many languages.
Website: http://www.gimp.org/
Xara Extreme
Xara Xtreme for Linux is a powerful, general purpose graphics program for Unix platforms including Linux, FreeBSD and (in development) OS-X.
Formely known as Xara LX, it is based on Xara Xtreme for Windows, which is the fastest graphics program available, period. The Xara Xtreme source code was made available open-source in early 2006, and is being ported to Linux. This process is almost complete and Xara Xtreme for Linux is available for download now.
Website: http://www.xaraxtreme.org
Inkscape
An Open Source vector graphics editor, with capabilities similar to Illustrator, CorelDraw, or Xara X, using the W3C standard Scalable Vector Graphics (SVG) file format.
Website: http://www.inkscape.org/
Blender
Blender is the free open source 3D content creation suite, available for all major operating systems under the GNU General Public License.
Website: http://www.blender.org/
Moonlight 3D
Moonlight|3D is a free modern, flexible and extensible modelling and animation tool developed by a small but dedicated team. The goal is to provide a tool that is capable of turning even the most advanced and challenging projects of artists and technical artists into reality.
Website: http://www.moonlight3d.eu/cms/
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 which is compatible with Java 5 or later.
Website: http://www.artofillusion.org
K-3D
K-3D is free-as-in-freedom 3D modeling and animation software. It features a plugin-oriented procedural engine for all of its content, making K-3D a very versatile and powerful package.
K-3D excels at polygonal modeling, and includes basic tools for NURBS, patches, curves and animation
Website: http://www.k-3d.org/wiki/Main_Page
Archimedes
Archimedes is a computer-aided design software focused on architecture. It is developed by a team of Computer Science students with colaboration of student and professional architects. The project was first conceived of on June 2005, but actual development only started on March 2006. At its first stage, the project aims to be a simple drawing board for architects. With this, it would be approximately equivalent to the most popular program among architects.
Website: http://archimedes.incubadora.fapesp.br/portal
BRL-CAD
BRL-CAD is a powerful cross-platform open source solid modeling system that includes interactive geometry editing, high-performance ray-tracing for rendering and geometric analysis, image and signal-processing tools, a system performance analysis benchmark suite, libraries for robust geometric representation, with more than 20 years of active development.
Website: http://brlcad.org/
OpenFX
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.
Website: http://www.openfx.org
Pixie
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).
Website: http://www.renderpixie.com/
Dia
Dia is roughly inspired by the commercial Windows program 'Visio', though more geared towards informal diagrams for casual use. It can be used to draw many different kinds of diagrams. It currently has special objects to help draw entity relationship diagrams, UML diagrams, flowcharts, network diagrams, and many other diagrams. It is also possible to add support for new shapes by writing simple XML files, using a subset of SVG to draw the shape.
Website: http://live.gnome.org/Dia