The beauty of OpenSCAD

All the CAD software I have used in the past was based on a GUI. AutoCAD does include a language so you can type commands and create macros too. But the way OpenSCAD is surprising (to me) and very useful: You "program" the objects you want to create. It is all based on a scripting language and the concept of constructive solid geometry. You can define basic shapes, like cylinders, spheres or cubes and then operate them to obtain the design you need.

You can experiment with this technology in Java3D too.

Once you have created your design, you can save the result as a variety of file formats, including STL. STL format is supported by most 3D printing tools, including Reprap project software tools (and Skeinforge). Many of the objects available in Thingiverse.com have been created this way.