FeenoX

FeenoX is an open-source engineering solver for mathematical and finite-element problems, built around editable text inputs rather than graphical modeling. It is best suited to advanced engineers, Unix-oriented developers and researchers who want to automate analyses or run them in parallel. Choose it for a flexible GNU/Linux workflow; look elsewhere if a graphical desktop interface is essential.

Overview

The solver covers dynamical systems expressed as ODEs or DAEs, alongside heat conduction, thermo-mechanical analysis, modal analysis, neutron diffusion and neutron transport. Because problem definitions live in self-descriptive, English-like files, users can revise an analysis without recompiling. That favors repeatable, scriptable work, but assumes comfort with constructing and managing technical inputs.

FeenoX is free and open source under the GNU GPL version 3 or later, which permits use, modification and redistribution under its terms. Its source and dependencies are open, and the project provides unit, regression and mathematical or code verification tests. The license disclaims warranty to the extent permitted by law.

Key features

Inputs, solvers and results

FeenoX reads meshes in Gmsh's .msh format and can write results as Gmsh MSH or ParaView VTK/VTU files. It uses GNU GSL, SUNDIALS, PETSc and SLEPc for computation. This makes it a sensible fit for teams already working with those libraries and post-processing formats; it is less compelling for users seeking a self-contained visual modeling environment.

Parallel and connected workflows

MPI parallelization supports workloads spread across multiple computers, and the design targets scalable remote servers. Its API-oriented approach also supports integration with web interfaces, REST APIs, large language models, standard post-processing tools and Markdown or LaTeX reporting. Users can reach it through browser-based interfaces such as SunCAE and CAEplex, though FeenoX itself has no graphical interface.

Pricing

FeenoX is free: the FeenoX plan costs nothing and is open-source software under the GNU GPLv3+ license. The Free plan also costs nothing, with no paid pricing stated. There is no paid tier to weigh against a feature-limited free version; the main trade-off is operational. Generic statically linked GNU/Linux binaries omit MUMPS and MPI and use only basic optimization flags, so users who need those capabilities should consider another installation route, such as supported Debian or Ubuntu packages or building from source.

Platforms

The project targets GNU/Linux and is not expected to run in Windows. It is available in Ubuntu 25.04 onward, with official installation options including Debian or Ubuntu packages, generic statically linked GNU/Linux binaries, source tarballs and the GitHub repository. The binaries are convenient to obtain, but their MPI and MUMPS omissions matter for parallel or solver-dependent workloads. Web-based interfaces provide another access route without changing the underlying Linux focus.

Who it's for

FeenoX is aimed at advanced users, including industry engineers, Unix hackers and academic professors. It suits people who can work with plain-text problem definitions, Gmsh meshes and technical post-processing, especially when automation or parallel computation matters. Those who need visual authoring, a Windows desktop application or point-and-click setup should choose a different tool.

Pros and cons

• Broad engineering coverage: ODEs and DAEs sit alongside thermal, mechanical, modal and neutron analyses, making it useful across several technical problem types.
• Automation-friendly inputs: English-like text definitions can be changed without recompiling, which supports repeatable workflows and integration.
• Open and verifiable: GPLv3+ licensing, open dependencies and unit, regression and verification tests offer transparency and freedom to adapt the software.
• No native GUI or Windows target: Users who expect graphical authoring or a Windows desktop workflow will need another option.
• Generic binary compromises: The static binaries lack MPI and MUMPS and use basic optimization flags, limiting their fit for some demanding computations.

Alternatives

OpenSim is another free, open-source option if support for macOS or Windows is important; downloading it requires a SimTK account. SimFlow is worth considering for readers seeking a freemium option with a free trial and Linux, macOS, web and Windows platforms; its free plan is shown as free, with no signup and no USD price displayed to our checker.

ngspice is a free circuit simulator for command-line or file-based work, but it has no schematic entry. COMSOL Multiphysics is a paid option with a free trial and a perpetual license priced by quotation. Xcos is a free, open-source option distributed with Scilab for Linux, macOS and Windows. FEST-3D is free and GPLv3-licensed for Linux and macOS. MPTRAC is an open-source Linux option with installation from source or binaries and a browser-based Web Runner. myPhysicsLab offers free browser simulations, Apache 2.0 source code and downloadable offline versions.

Verdict

Choose FeenoX if you need a free, adaptable engineering solver whose text-based workflow can scale into automated and parallel computing. Its breadth and open implementation are strong reasons to adopt it, but the lack of a GUI and the limitations of its generic binaries make it the wrong fit for users who need visual modeling, Windows support or MPI out of the box.