google-deepmind/mujoco ? reverse-engineered prompt

Build me a fast physics simulator for articulated robots and other connected mechanical systems, something like MuJoCo.

I want it to let me load a model, run accurate motion and contact simulation, and view the result in a simple interactive window. It should feel like a research tool, so include a clean C API, a native viewer, and support for Python so I can script experiments without writing everything in C++. If it makes sense, also include a small demo app that opens a scene and lets me play, pause, and inspect the simulation.

Please set it up so it can be built from source on the main desktop platforms, and make sure the basic examples work out of the box. If you need to check current build or install details, look up the latest docs online and follow the usual best practices for a project like this.