The following programs are for 3D design and animation. All of these, with the exception of SketchUp are completely free and open source. SketchUp has a limited free version, that is still a good functional option.
Blender is a 3D animation and design program. You can draw and manipulate objects in a 3D space. Full-length, animated movies have been created with Blender. Games have been created with Blender, as well as realistic inanimate objects. There are really great communities online with repositories where you can find 3D art that you can use in your own animations.
Sweet Home 3D
This is a program with which you can design a house or building layout. Its a simple program in which you design in a 2D space and the program creates a 3D model of your design. You can place furniture in your design as well as design the exterior.
BRL-CAD and FreeCAD
This program is very similar to AutoCAD and will have a lot of the same features. BRL-CAD has been extensively used by the military. Its a great program for designing and rendering objects.
FreeCAD is another program that is similar to AutoCad and is a great program to design in a 2D format and render 3D.
I included SketchUp because it is still free for personal use and its an easy program to use to draw objects. Its a 3D modeling program that can be used for architecture, interior design, engineering, or film and video game design. Its owned by Google and there is an online library of free model assemblies to which users may contribute models. Its available for Windows 7 and later and OS X 10.9 and later.