I have tested the Unity Game Engine and it is quite interesting for architectural visualization. This engine works on Windows and on Mac OSX, can create standalone or web-applications and you can even create WII and iPhone games, but then you need the Pro-version + additional (non-free) modules. I have been playing with the OSX version and it takes some (not that much) learning to get started. Try the help files and the video tutorials on the Unity site and you are ready to go. The free version, which is very complete, misses realtime shadows, which is quite frustrating. You could try baking in your shadows using Lightmaps, which is possible in must up-to-date DCC programs, such as 3ds Max, Maya, Cinema4D and even Blender. The following part is a small example (provided you have installed the Unity player for your browser. The whole scene was modeled in ArchiCAD 12, exported to Cinema4D 11.5, exported into FBX and loaded into a simple Unity Scene. After some attempts I got it working ...
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