Since the subject was brought up in another topic, I thought I would make it a topic itself. A few companies have started to offer drafting and 3d design software for free (in hopes you will eventually purchase one of their products)
QCad; Matthias Melcher mentioned using the shareware QCad, which is 2d Only.
Alibre Design; I've worked a bit with Alibre Design. They have a freeware "Alibre Express" which does 3-d parametric design. This is a very professional, full package. The Express version is limited to 3 parts in an assembly, and requires that you maintain an internet connection which will provide advertisements. ($50 to turn off the ads).
Solidedge; Another freeware 2D program is offered by Solidedge. I haven't used it.
Anyone else want to add to the list?
Joe Dunfee