There is a new online CAD software that allows free use. With Onshape you can design parts, assemblies and drawings. The basic account is free and limits the number of projects (currently 10) you can create that remain private (only you can see them). The rest will be public so that anyone with an Onshape account can access and use them. They also offer a professional account for $100/month that allows all your files to remain private.
They’re also working with other OEMs to bring added functionality into the cloud based software like CAM and finite element analysis.
Check it out at http://www.onshape.com