LeoCAD is a 3D CAD program for creating virtual LEGO models by using parts from LDraw library, developed by Leonardo Zide in 1997, using C++. It's free and open-source, and works on Windows, Mac and Linux platforms. It enables users to create their own LEGO models as they wish.

3D-Tool is a versatile and universal tool for visualizing, analyzing and converting 2D/3D CAD model files, developed by 3D-Tool GmbH & Co. KG from Germany. It is capable of importing and reading all common 3D and 2D CAD data interchange formats and some native CAD file formats, and provides various operations for visualizing, analyzing, marking, and collaborating CAD projects. Thus, you can do in-depth analysis of assemblies or individual parts and develop solutions.

VariCAD is a lightweight, comprehensive, fast, and user-friendly 2D/3D CAD system from Czech Republic, specially designed for mechanical and electrical engineering design. It enables designers to quickly create, evaluate, and modify their models by providing users with everything necessary for mechanical designing work.