SceneCaster is launching its service today that makes it not too difficult for anyone to build a virtual room and then stock it with furniture and decorations.
It's not a virtual world. There are no in-scene avatars (at least not in this version). All it does it let you build interactive scenes. But it's very interesting, and potentially useful. For example, if you want to create an interactive representation of your retail shop to embed on your store's site, this is the tool for you. Users can then fly around the room and see things from any angle.
Also, if you want to see what your room will look like with new furniture, you can use SceneCaster's rich database of furnishings (it interfaces to Google's library of SketchUp drawings) and try things out in the room you've built. What's cool, from a business perspective, is that SceneCaster links these items to online commerce. So if you really like that virtual Eames chair in your virtual room, you can more easily buy the real thing. SceneCaster, of course, extracts some revenue for itself from these links.