OpenSCAD lends itself to be treated as a function/stand alone program for generating models as well. Some of the 3D modeling websites even have OpenSCAD integration that runs it in your browser to generate the model based on the flagged configurable parameters. That’s powerful for basic functions like the mentioned adapters, because you can have a page that just spits out adapters of any size and shape.

Theoretically, a more standard CAD program like FreeCAD can use OpenSCAD for a standard parts library like threads, screws, bolts, sprints and allow for custom creation of those outside the standard. FreeCAD has some OpenSCAD support, but I’m not sure if it uses it in that way.