Sweet Home 3D - a free interior design app
And yes, it's fun. Oh, and so useful! Ever wondered how the black leather couch will fit in your living room? Or should you give a red wall color in your kitchen a try? It will take you an evening to figure out how the program works but than you can easily reproduce your flat and try different configurations, colors and furniture. The limits are on the lights effect over colored objects and the fact that you cannot group several objects to create your own piece of furniture and then move it and turn it as a single object.
Sweet Home 3D may be run under Windows 98 to 7, Mac OS X 10.4 (Tiger) to 10.6 (Snow Leopard), various Linux systems and Solaris. Depending on whether Java is installed on your system or not, you may launch the program with Java Web Start or its installer. All download mirrors and additional files may be found here.