Algodoo by Algoryx - free and commercial 2D-simulation software designed in a playful, cartoony manner used to creat technical interactive scenes.
Blender - free and open-source 3D content-creation program for modeling, rigging, animation, simulation, rendering, compositing and motion tracking, even video editing and game creation.
Inkscape: Draw Freely - free and open-source vector graphics editor; it can be used to create or edit vector graphics such as illustrations, diagrams, line arts, charts, logos and complex paintings.
