Where to Actually Find Free Engineering Software — 19 Sources and How to Check a Licence

The problem with searching "free software for…" is that the first results almost always lead to the same "Best Free X 2026" sites — sponsored listings that call a trial period free. The genuinely free tools do not pay for placement, so they are not there.

Here are the sources this directory is actually built from, ordered by how well they filter. All of them were checked.

Government repositories — the highest quality

This is the important category. Software developed with public money is usually released into the public domain, with source code, full documentation and a validation history. There is no "free edition" here — the software is free.

USGS Software — hydrology, geology, seismology and mapping. The source of the USGS entry in this directory.
USACE HEC — home of HEC-RAS and HEC-HMS, the global standard in hydraulics.
US EPA — EPANET and SWMM, the engines underneath most commercial water and drainage packages.
DOE CODE — everything funded by the Department of Energy, with an explicit licence on every item. That is exactly what is hard to find elsewhere.
NREL — renewables, wind, solar and building energy. The source of OpenFAST.
LBNL Simulation Research — EnergyPlus, Radiance and the Modelica Buildings Library.
LBNL Windows & Daylighting — WINDOW and THERM for glazing and thermal bridges.
FHWA Geotechnical — retaining walls, piles and slope stability.
NIST — metrology, materials, fire safety and statistics.
WBDG Tools and OSTI — two further broad collections.

Curated professional directories

BEST Directory (IBPSA-USA) — the most complete building energy software directory there is, filterable by capability. The best in its field.
OSGeo — the whole open GIS world: QGIS, GRASS, GDAL, PostGIS.
CFD Online — the oldest and most complete list of CFD solvers, meshers and post-processors.
Debian Science — sorted by discipline. Everything is open by definition, because that is the entry requirement.
CAELinux — a distribution bundling Code_Aster, Salome, Elmer and OpenFOAM. An excellent map of the ecosystem.

General repositories — for discovery, not verification

SourceForge — large, weakly filtered. Useful for finding a name, not for verifying a licence.
GitHub Topics — swap the topic: cfd, cad, gis, structural-analysis. The most current there is, because it is the source itself.
Joinup — open source from the European public sector. A non-American angle, and worth checking for that reason.

How to check a tool is really free — four questions

This is the test every entry in this directory goes through:

Who may use it? "Free" and "free for students" are completely different things. If there is an eligibility condition, it must be stated.
What may you do with it? Is commercial use allowed or not? This is the question most people miss, and then discover it mid-way through a paid project.
Is there a time or resource limit? "Try for free" is not a free licence. A compute-hour quota or a project count is a limit too.
Where is your work stored? On free cloud tools such as Onshape and SimScale your work is public. That is not fine print — it is a business decision.

And two warnings that keep coming up: download only from the vendor's own site. A site offering a "download mirror" or a "full version" of commercial software is distributing malware, not software. And the codes built into American tools are not your local code — the engine is right, the threshold requirements are local.

And if you find something missing here

This directory is built partly from suggestions by engineers and students who use these tools in practice — and that is the kind of information search engines are bad at surfacing. If you come across a good free tool, send us the link. Every suggestion is checked by hand against the four questions above before it is published.

All software in the directory · search by field, licence and platform