Roomtodo - Simple yet powerful online tool for interior design and floorplans with built in walkthrough module.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Sweet Home 3D - Sweet Home 3D is a free interior design application that helps to draw the plan of house, arrange furniture on it and visit the results in 3D.
InnoPlanner - InnoPlanner is a commercial based interior designing software.
SketchUp - 3D for Everyone
FreeCAD - An open-source parametric 3D modeler