FreeCAD is a general-purpose parametric 3D modeler for CAD, MCAD, CAx, CAE, and PLM, aimed directly at mechanical engineering and product design but also fits a broader range of uses in engineering, such as architecture.
Art of Illusion
Art of Illusion is an open-source 3D modeling and rendering studio. Many of its capabilities rival those found in commercial programs. Highlights include subdivision surface-based modeling tools, skeleton-based animation, and a graphical language for designing procedural textures and materials.
Clara.io is a web-based 3D modeling, animation, and rendering tool that allows you to create complex 3D models and photorealistic renderings and share them without installing software on your device.
Tinkercad is a web-based online 3D modeling program for creating models for 3D printing as well as an entry-level introduction to constructive solid geometry in schools.
SculptGL is a web-based 3D modeling and sculpting program. If you want to create a 3D game or video character models that are detailed and unique, SculptGL is a simple and good tool.
Blender is a free and open-source 3D computer graphics software used to make animated films, visual effects, art, 3D printed models, motion graphics, interactive 3D apps, virtual reality, and computer games.