[dogma1138]

PhysX isn't Open Source only the free SDK is, all the stuff that actually makes PhysX work is proprietary and is part of NVIDIA GameWorks.

Havok isn't just a physics engine although Havok Physics is probably the most used middleware that Havok makes.

Which is better well it depends, PhysX is supported by more 3rd parties, but you can only have dedicated processing on CUDA enabled GPU's, PhysX supports both AMD and NVIDIA GPU's and probably in the future Intel and maybe mobile ones.

Overall more games use PhysX these days than Havok, it was the defacto standard in the previous decade but not so much today, I don't think a single game came out this year which uses Havok.

[maccard]

Many of the big hitting AAA games use Havok. Although they haven't launched yet, assassins creed, fallout, Halo, just cause 3. There were plenty last year like Destiny, watch dogs, evil within, shadow of mordor.