Autodesk Homestyler is a good website for designing the interior of a room or of an entire house. The service is free and can be used without registering for an account (although registering for an account is an option). Using Autodesk Homestyler you can design the shape of a room, add closets, remove or add walls, and drop in furnishings. You can view your designs in 2D or 3D. In 3D you can rotate your room to get a better picture of the layout of your room.

Applications for Education
Autodesk Homestyler is designed for use by people who are remodeling or building a new room, but I thought that it could be used as part of mathematics lesson on area. You could give students an assignment to try to design a room in as many configurations as possible while still staying within a square footage parameter that you assign. You might also challenge students to see how many units of a particular furnishing can be placed in the rooms they design.