QCAD Community Edition
QCAD is an application for computer aided drafting in two dimensions (2d). With QCAD you can create technical drawings such as plans for buildings, interiors, mechanical parts or schemas and diagrams. QCAD works on Windows, Mac OS X and many Linux and Unix Systems. The source code of the QCAD community edition is released under the GPL (Open Source).
Proprietary alternative(s):
AutoCAD 2009
Open Source alternative(s):
BRL-CAD