• DesignWorkshop Lite

From author's site:

The complete freeware DesignWorkshop Lite software package provides all you need to build your own 3D models for home design and visualization of architecture, landscapes, exhibits, or any kind of spatial design.

With DesignWorkshop Lite you can view and walk-through ready-made models of any size, like the free 3D building models in the Great Buildings Online, in DXF, DesignWorkshop, or 3DMF format, with amazing live 3D speed.