Software CAD

Overview

See CAD Discussion and CAD

Here are some open source options for CAD. Because the open-source options for CAD are rather limited (there are currently no good open source parametric 3D CAD programs), significant closed-source programs are also listed at the end.
Open Source
Wings 3D
Sweet Home 3D
Antimony
Blender

Mesh-based direct modelling. Not parametric.
Focused on artistic 3D modelling and animation.
No CAD functionality so it is not suited to CAD use, though it can be used for very basic prototyping.

FreeCAD

The most promising open source 3D-CAD software by far, but still has some way to go. The recently (Nov. 2013) added assembly module is a decisive step forward allowing productive work. [1]
Focused on mechanical engineering and product design.
Feature-based, parametric, with 2D sketch input with constraint solver.
Based on OpenCasCade and Coin3D (an implementation of Open Inventor).
Windows, Mac OSX and Linux.
Supports brep, nurbs, booleans operations or fillets.
"A modular architecture that allow plugins (modules) to add functionality to the core application. Those extensions can be as complex as whole new applications or as simple as python scripts or self-recorded macros."
Built-in python interpreter for macros and scripts.
Import/export to standard formats such as STEP, IGES, OBJ, DXF, SVG, U3D or STL.

Art of Illusion

Focused on animation
Import from OBJ STL SVG SVZ export to POV OBJ STL

Salomé

Focused on numerical simulation, but can apparently also edit CAD data.

BRL-CAD

BRL-CAD is a powerful cross-platform open source solid modeling system that includes interactive geometry editing, high-performance ray-tracing for rendering and geometric analysis, image and signal-processing tools, a system performance analysis benchmark suite, libraries for robust geometric representation, with more than 20 years of active development. Operating Systems: All major platforms.
Focused on analysis, rather than modelling (specifically ballistics research).
CSG-based - models are built via combinations of basic shapes like spheres and cones, rather than extruded from arbitrary sketches.
Very old code base.
Actively developed.

avoCADo

Abandoned since 2008.

QCad Community Edition

Available only as source code
How to get support for the QCad Community Edtion?
2D only.
Frustrating UI.

LibreCAD

LibreCAD is a fork of the QCad Community Edition
Available for Linux, OSX and Windows
The 1.0.0 series is still based on QT3
The forthcoming 2.0.0 series is based on QT4

OpenSCAD

Procedural script-based 3D-CAD (there is no editor GUI).
Uses CSG (constructive solid geometry) internally and can generate STL but also *import* STL (and use CSG on the resulting model). It also can read 2D designs in DXF and extrude parts of it into the 3rd dimension (extrusion can be linear or on different paths, so you can make, e.g., a torus by extruding a circle on a circular path).
Suitable for very simple shapes which benefit from being parametrically defined, e.g. gears, fasteners, wheels, etc.
Unsuitable for complex models.

http://www.cannymachines.com/entries/9/openscad_dimensioned_drawings

ImplicitCAD

Procedural script-based 3D-CAD similar to OpenSCAD (there is no editor GUI).
Can generate STL and SVG and GCode files
Suitable for simple shapes which benefit from being parametrically defined, e.g. gears, fasteners, wheels, etc.
better suitable for more complex models than OpenSCAD.

pythonOCC

Object oriented script-based 3D-CAD (there is an editor GUI).
based on Open CASCADE. It can handle STEP (AP203 and AP214), IGES, STL (ascii/binary) and VRML.
It has parametric design, extrude/revolve/sweep as well as boolean operations, FE-meshing, rigid body simulation, but no 2D-drawing capability.
Operating Systems: Linux, Mac OSX or Windows.
The scripting commands are simple and powerful. As in openSCAD and FreeCAD the python scripts would allow for distributed version control to easily organize community collaboration with existing tools (like git or mercurial and free public git-hosting). Draw back is the lack of 2D-drawing capability.

HeeksCAD

Development halted.
Use the geometric constraints solver to create accurate drawings from rough sketches
Solid modeling is provided by Open CASCADE

HeeksCNC

CAD/CAM application written in Python that can help you produce the NC code for your milling machine.

OpenCASCADE

Open CASCADE Technology is software development platform freely available in open source. It includes components for 3D surface and solid modeling, visualization, data exchange and rapid application development. Operating Systems: Linux, Sun Sparc, or Windows.
Seems too clunky without a better GUI.

CADEMIA

CADEMIA is a modern CAD system with a full functionality for civil engineering and architecture.
2D only, focused on architecture.
It is written in Java and is available for Windows, Mac and Linux
Open source
It is available in English and German

Closed Source, Free
PTC Creo Elements Direct Modelling Express 4.0

Ridiculous name.
Limited to something like 50 parts per assembly. I believe that is the only limitation of the free version.
Direct extrusion-based modelling, similar to Sketchup but much more powerful.
Probably the best free CAD on Windows.
Windows only. Sort of runs in wine, but not usably (crashes often, UI flickers).

Google SketchUp

Focused on architectural sketching.
Free, but not open source, works in linux under Wine. See Sketchup on Linux for installation notes.
Direct modelling. Not parametric, and does not allow changing dimensions to exact values.
Better than Blender, but still not really suitable for CAD.

DesignWorkshop Lite

Only Windows & Mac versions
For home design and visualization of architecture, landscapes, exhibits, urban design, or any kind of spatial design

DraftSight

Good AutoCAD compatibility.
Focused on 2D drafting, very little 3D support.

gCAD3D

free but closed sourced 3D CAD/CAM system
prametrized, scriptable
CNC processor
Linux, Windows OS

VariCAD

low priced (~600$) full featured 3D/2D CAD
free viewer available for VariCAD and STEP files
integrated calculation tools for springs, bolt preloading etc.
STEP I/O and much more
Linux, Windows OS
partially applied on GVCS backhoe and trencher (use OSE Wiki search)

Closed Source, Expensive
Solidworks

Extremely popular and powerful history-based parametric 3D CAD.
Modern usable UI.
Price in the £1000-range.
Windows only. Can be started in wine, but not usable.
Focused on mechanical engineering and product design. Not suited to architecture.

Onshape

Parametric modelling.
Modern usable UI.
Online tool.
Price ~$100/month.
Focused on mechanical engineering and product design.
Developed by ex-solidworks guys.

Pro Engineer

Main competitor to Solidworks.
Used to run on Linux natively, new versions are Windows-only. The last Linux version was Pro/E Wildfire 4
Archaic Motif GUI.
Modelling paradigm essentially identical to Solidworks.
Now known as "Creo Elements/Pro" (I'm unsure if it is based on the same code as Pro/E was).

SolidEdge

Solidworks competitor from Siemens.
Parametric feature-based modelling.
Windows only.
Has a free 2D drafting option

Autodesk Inventor

Another solidworks competitor.
Windows only.

AutoCAD

Originally 2D-only and it shows.
More architecturally-focused than Solidworks and Pro/E.
Originator of the DXF format.
Used to be the industry standard. Much less so today.

NX

Super high-end CAD from Siemens.
Very similar to Solidworks. If you have used one it will not take long to learn the other.
Price is "it doesn't matter if you ask or not - you can't afford it". This is what they use to design nuclear submarines.
As a result, Googling for help is no use.
Runs on Linux natively.

Unknown

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