Free, Libre & Open Source Software
The following organisations offer free and/or open source software which is essential to progressive architects:
Operating System : Ubuntu GNU/Linux : http://ubuntu.com
Office Suite Software (Linux, Windows & Mac OS) : http://www.libreoffice.org
2D CAD : Free Alternative to AutoCAD LT : http://doublecad.com (1)
3D CAD : FreeCAD : http://www.freecadweb.org/ (2)
Interiors : Sweet Home 3D : http://sourceforge.net/projects/sweethome3d/
(1) DoubleCAD XT can be run in Windows or in Linux with a Windows Emulator.
(2) FreeCAD is a general purpose feature-based, parametric 3D modeler for CAD, MCAD, CAx, CAE and PLM, aimed directly at mechanical engineering and product design but also fits a wider range of uses in engineering, such as architecture or other engineering specialties. The Arch workbench provides modern BIM workflow to FreeCAD, with support for features like IFC support, fully parametric architectural entities such as walls, structural elements or windows, and rich 2D document production. The Arch workbench also feature all the tools from the Draft Workbench. It is 100% Open Source (LGPL2+ license) and extremely modular, allowing for very advanced extension and customization.
Free Software is today an intelligent, functional, practical, economical and well supported reality thanks to the pioneering work and subsequent success of Dr Richard Stallman and the Free Software Foundation : https://stallman.org/ / http://fsf.org