For parametric CAD, there's Solvespace. GPL'd as of version 2.0. I like it better than OpenSCAD, and the price is equally right. I don't know why, but it doesn't get much attention.
Just checked it out...on Linux. Cross-plateform packages have been posted to their forum. Solvespace is fairly intuitive and quite functional. Happy to have found it.
Linux: http://solvespace.com/forum.pl?action=viewthread&parent=574
OSX: http://solvespace.com/forum.pl?action=viewthread&parent=586