MuJoCo

The engine provides a free, open‑source physics simulation platform designed for research and development in robotics, biomechanics, graphics, animation, and other domains that require fast, accurate modeling of contact‑rich dynamics. It supports generalized‑coordinate simulation, inverse dynamics that remain well‑defined during contacts, and a continuous‑time formulation of constraints solved via convex optimization. Users can model soft contacts, limits, dry friction, equality constraints, as well as particle systems, cloth, rope, and other deformable objects.

A range of actuators—including motors, cylinders, muscles, tendons, and slider‑cranks—are available, together with selectable solvers (Newton, Conjugate Gradient, Projected Gauss‑Seidel) and friction cone representations (pyramidal or elliptic). Numerical integration can be performed with Euler or Runge‑Kutta methods, and the engine offers multi‑threaded sampling and finite‑difference approximations for computationally intensive techniques such as optimal control, state estimation, system identification, and automated mechanism design.

Models are defined in an intuitive XML format (MJCF) and compiled by a built‑in compiler. A cross‑platform GUI provides interactive 3‑D visualization using OpenGL, while the runtime module is written in ANSI C and hand‑tuned for performance, making the engine suitable for both scientific validation and interactive applications.