CAD software, or computer-aided design software, is a tool used by designers and engineers to create, modify, analyze, and document 2D drawings and 3D models of physical objects. It enhances productivity, accuracy, and collaboration in the design process across various industries.
LibreCAD (librecad.org)
LibreCAD is a free, open-source, and extensive 2-dimensional (2D) computer-aided design program that is specifically designed for professionals who create industrial designs as well as for those who are looking for affordable or even free drawing tool that can be used in their small design projects. As the name implies, the program only provides 2D capabilities and lacks what a 3D solution has to offer. But it has almost everything a user or an artist needs when it comes to creating complex designs. It is also compatible with and supports commonly used Operating Systems (OS) including Windows, different versions of Linux, as well as MacOS.
LibreCAD is a branch from an earlier version of QCAD. It is noticeably different or lacking in some areas but is still a very good program.
NOTE: LibreCAD is not related to LibreOffice.
QCAD (qcad.org)
QCAD is a free, open source application for computer aided drafting (CAD) in two dimensions (2D). With QCAD you can create technical drawings such as plans for buildings, interiors, mechanical parts or schematics and diagrams. QCAD works on Windows, macOS and Linux.
FreeCAD (freecad.org)
FreeCAD is an open-source parametric 3D modeler made primarily to design real-life objects of any size. Parametric modeling allows you to easily modify your design by going back into your model history and changing its parameters.
FreeCAD is made primarily to design objects for the real world. Everything you do in FreeCAD uses real-world units, be it microns, kilometers, inches or feet, or even any combination of units. FreeCAD offers tools to produce, export and edit solid, full-precision models, export them for 3D printing or CNC machining, create 2D drawings and views of your models, perform analyses such as Finite Element Analyses, or export model data such as quantities or bills of materials.
BRL-CAD (brlcad.org)
BRL-CAD is a powerful open source cross-platform solid modelling system that includes interactive geometry editing, high-performance ray-tracing for rendering and geometric analysis, a system performance analysis benchmark suite, geometry libraries for application developers, and more than 30 years of active development.
OpenSCAD (openscad.org)
OpenSCAD is software for creating solid 3D CAD models. It is free software and available for Linux/UNIX, Windows and Mac OS X. Unlike most free software for creating 3D models (such as Blender) it does not focus on the artistic aspects of 3D modelling but instead on the CAD aspects. Thus it might be the application you are looking for when you are planning to create 3D models of machine parts but pretty sure is not what you are looking for when you are more interested in creating computer-animated movies.
OpenSCAD is not an interactive modeller. Instead it is something like a 3D-compiler that reads in a script file that describes the object and renders the 3D model from this script file. This gives you (the designer) full control over the modelling process and enables you to easily change any step in the modelling process or make designs that are defined by configurable parameters.
OpenSCAD provides two main modelling techniques: First there is constructive solid geometry (aka CSG) and second there is extrusion of 2D outlines. Autocad DXF files can be used as the data exchange format for such 2D outlines. In addition to 2D paths for extrusion it is also possible to read design parameters from DXF files. Besides DXF files OpenSCAD can read and create 3D models in the STL and OFF file formats.