LibreCAD

BRL-CAD is an open-source, cross-platform solid modeling system that includes interactive geometry editing, high-performance ray-tracing for rendering and geometric analysis, and geometry libraries for application developers.

SolveSpace is an open-source 2D/3D constraint-based parametric computer-aided design software that supports basic 2D and 3D constructive solid geometry modeling.

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 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.

Daz Studio is a 3D scene creation and rendering application for producing 3D models, animations, and more to create your realistic universe.

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.