Endorphin is a dynamic motion synthesis software package developed by NaturalMotion. Endorphin can be used to generate computer simulations of large numbers of independent characters interacting with each other and the world according to brief scripts or 'behaviours'. It combines physics, AI, and genetic algorithms to create realistic animations. Unlike Euphoria, also developed by NaturalMotion, Endorphin is not an engine, but a 3D animation tool for Microsoft Windows. It has been used in many movies and video games such as Troy, Poseidon and Tekken 5.