OpenSCAD is a software for creating solid 3D CAD objects.
Unlike most free software for creating 3D models (such as the famous application Blender) it does not focus on the artistic aspects of 3D modelling but instead on the CAD aspects. Thus it might be the application you are looking for when you are planning to create 3D models of machine parts but pretty sure is not what you are looking for when you are more interested in creating computer-animated movies.
It is free software and available for Linux/UNIX, MS Windows and Mac OS X.
The version 3.5 of Unity has been released. 3.5 is one of the biggest releases to-date. It’s packed full of new features and improvements.
Major new features are:
Arbaro is a free tree generator. It's written in Java, so you can use it with any OS, wich is supported by Java.
Arbaro reads in an XML file with the tree parameters and writes out Povray, DXF or Wavefront OBJ files.
16 free 3D trees are included as XML-files ready for export.
You can download the Arbaro software from the project site at SourceForge.