PhysX SDK 4.0, an Open-Source Physics Engine

https://news.developer.nvidia.com/announcing-physx-sdk-4-0-an-open-source-physics-engine/

PhysX has been the market leader in physics simulations for more than a decade. The SDK holds the top spot due to continuous upgrades and optimizations; NVIDIA has ensured that PhysX is always ahead of the curve, enabling developers to deliver state-of-the-art physics simulations.