OpenSim

Overview

OpenSim is a free, open-source platform for modeling and analyzing how people, animals, robots, and their surroundings move and interact. It is best suited to research and teaching that depends on movement mechanics. Its mix of model-building and analysis tools is substantial, but the GUI’s operating-system limits matter if you need a Linux desktop workflow.

Key features

Build and inspect movement models

OpenSim’s graphical interface lets users visualize models and generate and analyze simulations. Models can combine rigid bodies, joints, constraints, contact, muscles, and other actuators, so the platform can represent both a system’s structure and the forces involved in its movement. 3D visuals support model inspection, while data export helps move results into other workflows.

Analyze motion and muscle action

Tools for inverse kinematics, inverse dynamics, static optimization, and forward dynamics address different parts of movement analysis. Computed Muscle Control can generate muscle-driven forward simulations. This makes OpenSim a strong fit for work that needs more than visualization, though its analysis suite is most useful to people studying movement rather than general-purpose simulation.

Script and extend

The API can be used through Matlab, Python, Java, and C++, and the GUI includes an embedded Jython shell for scripting. Plugins can add analyses and model components, but must be built for the same OpenSim version and platform. That enables tailored workflows while making plugin compatibility a practical maintenance constraint.

OpenSim 4.0 added support for reading marker and force data from C3D files. The project also provides documentation, tutorials, and a discussion forum where users can seek help from experts. The GUI and API use the Apache 2.0 license; models, examples, and plugins may have separate licenses.

Pricing

OpenSim is free and open-source software. Its sole plan, OpenSim, costs nothing. There is no free trial because the software itself is free, and downloading it requires a SimTK account.

There are no paid tiers or published seat limits to weigh. The free plan suits academic, teaching, and commercial users who need its movement-modeling tools without a software charge. Users should account for the separate licenses that may apply to models, examples, and plugins.

Platforms

OpenSim is desktop software. Its GUI is distributed for 64-bit Windows and Mac, with no public Linux GUI distribution. The API source can be built for Windows, Mac, and Linux, so Linux users can work through the API but should not expect the standard graphical desktop application. API workflows are supported through Matlab, Python, Java, and C++.

Who it's for

OpenSim is aimed at research and teaching, particularly when a project needs to model and analyze movement in humans, animals, or robots. The project also welcomes commercial applications. It is a good choice for users who need detailed movement analysis, scripting, or custom model components; it is less suitable for those who require a Linux GUI or cannot manage version- and platform-matched plugins.

Pros and cons

• Pros: A free, Apache 2.0-licensed GUI and API provide a capable foundation for movement modeling, with a range of analysis methods and scripting options.
• Pros: Models can include bodies, joints, contact, muscles, and other actuators, and the platform supports 3D visualization, data export, and C3D marker and force data.
• Pros: Documentation, tutorials, and a discussion forum offer support for learning and troubleshooting.
• Cons: The public GUI is limited to 64-bit Windows and Mac, ruling out a standard Linux desktop experience.
• Cons: Plugins must match both the OpenSim version and platform, which can complicate upgrades or sharing custom extensions.
• Cons: Models, examples, and plugins may use licenses distinct from the Apache 2.0 license for the GUI and API.

Alternatives

Xcos is another free, open-source option distributed with Scilab, and supports Windows, Mac, and Linux. It may suit readers seeking a cross-platform alternative, while OpenSim is the more directly supported fit when human, animal, or robot movement modeling and analysis are central.

SimFlow offers a free plan, a free trial, and Linux, Mac, Windows, and web platforms. Consider it when those platform options matter more than OpenSim’s movement-analysis focus.

FeenoX is a free GNU GPLv3+ option targeting GNU/Linux, with API, web, and self-hosted availability but no graphical interface. It may fit users comfortable without a GUI; OpenSim is the better match for those who want its desktop visualization and movement tools.

FDTDX is free and open source for research, development, and commercial use, with Linux and self-hosted platforms. It is an alternative to consider if those deployment options fit your work.

DynamicalSystems.jl is free, community-built, and open source, with Windows, Mac, and Linux support. Choose it as an alternative when those qualities matter more than OpenSim’s movement-focused modeling and analysis.

myPhysicsLab offers free browser simulations, Apache 2.0 source code, and downloadable offline versions. It may suit readers looking for browser-based physics simulations rather than OpenSim’s movement-analysis workflow.

Open Source Physics is a free alternative available for web, desktop, and mobile platforms.

PhysSandbox provides more than 609 interactive simulators on the web, with no registration or paywalls. It may be a better fit when ready-made browser simulators are the priority.

Browse more options in Physics Simulation Software.

Verdict

Choose OpenSim if your research, teaching, or commercial work requires modeling and analyzing movement, and you value a free platform with an API and broad scripting support. Its main drawback is the lack of a public Linux GUI, alongside plugin compatibility requirements. If either constraint conflicts with your workflow, consider an alternative better suited to your platform or simulation needs.