The Open Physics Abstraction Layer (OPAL) is an open source realtime physics engine API similar to PAL. It was originally supported only ODE, but should be extendable to run off of multiple engines. OPAL is free software, released under both the LGPL and the BSD license.

OPAL is a high-level interface for low-level physics engines used in games, robotics simulations, and other 3D applications. Features a simple C++ API, intuitive objects (e.g. Solids, Joints, Motors, Sensors), and XML-based file storage for complex objects.

The latest version of OPAL is 0.4.0