The Silverlight Augmented Reality Toolkit (SLARToolkit) combined with rigid body physics and the Balder 3D engine powered by Silverlight 5's new hardware accelearated 3D API.
See the SLARToolkit project site for details:

Related blog post with details:
kodierer.blogspot.com/2011/06/cubelicious-silverlight-5-balder.html

SLARToolkit project site:
slartoolkit.codeplex.com

Background music is "Lullaby" by _ghost
ccmixter.org/files/_ghost/3631

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