To get a 2D CAD emerge qcad from
http://www.qcad.org/en
(you get the Community Edition) and do not forget the parts catalog emerge qcad-parts to get the stuff
in /usr/share/qcad-parts
. It uses the standard dxf file
format for the drawings. Qcad has a nice help.
Freemat from http://freemat.sourceforge.net/ is an other matlab alternative. It can be started as FreeMat and runs matlab code directly, smooth and well, it has some incompatibilities when it comes to plotting graphics.