Cry havok, and let slip the software of physics!
Havok Offers Core Physics Software Free for PC Game Developers has word that
the PC edition of Havok Complete will be released for free in May. Word is the
"award-winning physics and animation software product" is free to use for any
non-commercial project.
Now that Nvidia has bought AGEIA, we're bound to see that PoS PhysX merged into their cards, and probably quite a few developers shifting from Havok to PhysX.