Mechanical CAD Software

Solidworks
blender
unity

http://www.designworldonline.com/three-free-cad-programs-for-engineers-and-designers/
Solid Edge 2D Drafting
AutoCAD Inventor Fusion

Cadsoft Eagle Software – www.cadsoftusa.com

http://www.ehow.com/facts_7788150_cad-software-hobbyists.html

http://www.practicalmachinist.com/vb/cad-cam/cad-cam-software-beginner-136403/
To get an idea how a CNC machine tool controller works, download Mach3 from www.machsupport.com .
It will run on your machine as though its really controlling a machine, allowing you to run, write and play with G code. The concept of using it is similar to commercial machine tool controllers.

To get a feeling for the CAD/CAM side of CNC, download and go through the tutorials for demo versions of the following programs:

CAD:
Alibre from www.alibre.com
Rhino from www.rhino3d.com

CAM:
VisualMill from www.mecsoft.com
SheetCAM from www.sheetcam.com

You’ll be able the run the G code you create with the programs above on Mach3.

Draftsight
Alibre

http://www.techsupportalert.com/best-free-cad-computer-aided-design-programs.htm

http://www.techsupportalert.com/best-free-cad-computer-aided-design-programs.htm

http://www.techsupportalert.com/best-free-cad-computer-aided-design-programs.htm

http://umforum.ultimaker.com/index.php?/topic/4366-what-software-for-beginner/

http://cad.about.com/od/Personal_CAD/tp/Five-Top-Free-Cad-Packages.htm

http://computeraideddesignguide.com/5-best-free-cad-software-for-beginners/