gCAD3D is a complete and powerful 3D design application which will allow you to perform complex CAD projects. It is useful for both, professionals and novice users. This application has a wide range of design tools that will let you add all kinds of elements to your projects, view your objects from different angles and, edit and apply all kinds of textures, etc.
As you know, creation and design of 3D projects is usually performed by architects, designers, engineers and all of those professionals knowledgeable in complex models of structures and objects. So, if you are looking for a free yet powerful CAD application similar to commercial programs like AutoCAD, then I'm sure gCAD3D is one of the best options you could find. This amazing application features a program interpreter for geometry and NC-commands in 3D, an integrated 3D OpenGL viewer, an integrated NC-processor, and a programming interface for user programs. It has support for importing Step files and support for both importing and exporting Iges, DXF, and VRML files.
Definitely, gCAD3D is an excellent 3D design tool, it has many possibilities to compete against other commercial programs. But maybe the best feature is that the application is totally free, and can be downloaded for Windows and Linux.