The folks looking for a free and open source option for a Parametric 3D CAD have theirs choice now. HeeksCAD is a parametric 3D CAD, based on the open source modeler OpenCascade.
Actually it is for Linux and Windwos. It uses WX Widgets as its widget set.
The HeeksCAD site lacks on screenshots, as long as they are keeping a good work on the software... (let the community provides the screenshots ;-)
Googling a little we can found a good discussion in a forum at
http://www.linuxgraphic.org/forums/viewtopic.php?f=41&t=5728 (it is in French)
I had already used the Salome (another OpenCascade based tool), but the CAD it provides where more for geometry design for finite element pre and post processing. Diferent from Salome, HeeksCAD has much more functionalities from CADs like Pro/Engineer and SolidWorks.