One of the reasons I like CATIA over Solidworks is that I found there 3d modeling kernel to be more stable vs Solidworks.
Here is a kernel I think has a lot of potential.
Perhaps it can be used in the free CAD programs out there such as FreeCAD or openSCAD?
https://en.wikipedia.org/wiki/Russian_Geometric_Kernel
http://rgkernel.com/features-of-rgk.html
https://en.wikipedia.org/wiki/Geometric_modeling_kernel
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