Archimedes is a free and opensource CAD software. The interface is comfortable, fairly easy to use and is similar to commercial platforms. Exportable formats are svg (vector), pdf, xml and arc which is Archimedes’ native format. The downside is that documentation seems to be lacking and I maybe wrong here but there doesn’t seem to be a way to change the unit of measurement. With that said I still love it and will be using it.
You can learn more and download Archimedes here http://archimedescad.github.io/Archimedes/