It was so obvious that we thought we listed OpenSCAD for years already. Mistake finally corrected now.
Just the most efficient programmatic 3D solid modeller: you write code, and it translate to solid 3D.
Big community, big history, many application, free. Many have made parametric models, so that you just have to adapt one or several parameters and it adapts (typical case: a gear where you give module, width … and boom you have the precise 3D)
It is one of the REALLY rare tool that we promote that must be installed as it is not online. But it worth it.
Tipp: we also list in this directory its online fork, the “OpenSCAD playground“, just to test the principles, as it does not have 100% of the many features implemented and it may not be available there forever.