V-REP

A powerful 3D robot simulator, which features several versatile calculation modules (inverse kinematics, Physics/dynamics, collision detections, minimum distance calculations, path planning, etc.), a distributed control architecture (unlimited number of control scripts, threaded or non threaded), and several extension mechanisms (plug-ins, custom client application, etc.).

It offers a multitude of functionalities that can be easily integrated and combined through an exhaustive API and script functionality. V-REP comes in 5 different versions, with different licensing options for most versions.