You can create a "spreadsheet" with named cells and refer to those names in your constraints.

For example you could create a cell called "cylinderbore" and have either a static value in it, or a value computed from something else, and you could set a radius constraint to "cylinderbore/2", or "cylinderbore/2 + 0.3" or whatever you want.

There's a demonstration in this 5-minute video: https://www.youtube.com/watch?v=b07qbhYHZbU

(Contrary to what the video implies, you don't have to manually click on each constraint whenever you change your spreadsheet, the global recalculate button will do it.)

That's very helpful, I didn't know about this feature. I'll give it a try.

Since FreeCAD 0.17 one can do this with "Expressions". Click the Formula button in entry objects and you can make a formula that contains references like "someotherobject.propertyname".

For the central driving paramterss I recommend using a spreadsheet, as others have mentioned. I usually call that "inputs". And then have another one called "outputs" if I need to calculate something based on geometry, like total material/weights etc.

Hm. I'm not sure I follow and I use Fusion regularly and FreeCAD a little. Does the property editor/spreadsheet in FreeCAD not count? You change a value, the dependencies get recomputed. Works about the same as in Fusion and certainly satisfies "parametric" for me.

(I use Fusion too, and think it's overall easier to use and more polished, it just seems strange that the lack of parametricity is what irks you.)

As other folks have mentioned, you can make a spreadsheet and then use those variables. It's pretty clunky but it works.