Truespace is the product of Caligari, a company acquired by Microsoft recently. TrueSpace is a paid product before, but now they have released it as a freeware for windows. The new version of truespace allows people to export 3D content to virtaul earth. It also allows to export as X Format for game engines like XBOX 360. It serves as an alternative to 3ds Max and Google Sketchup. There is an open source project called Blender for 3D modeling which supports wide number of platforms including windows, mac, linux, BSD, solaris.
Download the application from here, you need to register for download. Thanks Amit Agarwal