Blender

blender

 

Gimp

http://www.gimp.org/downloads/

 

Openscad

http://www.openscad.org/

 

Freecad

http://www.freecadweb.org/

 

Slic3r

 

Cura

 

Netfabb

 

Repertier Host

 

MeshLab

 

123d design

 

Tinkercad

 

Meshmixer