[starseeker]

The other two projects that leap to mind for open source CAD are FreeCAD and BRL-CAD, but I'm not sure either would meet your particular requirements. I'm pretty sure BRL-CAD doesn't offer the sort of parametrics you'd want (the closest thing would probably be writing a procedural generator, which usually means C/C++ or a scripting language). I'm less sure about FreeCAD - they use the OpenCASCADE engine - but if the other commercial systems didn't offer what you want I'd be surprised if FreeCAD had it (not impossible though - it might be worth asking the dev team if your workflow could be realized in FreeCAD.)

Providing the STEP and STL files should cover pretty much what the open source CAD world is prepared to handle - FreeCAD can import STEP and BRL-CAD is working on it, and most 3D printing applications I know of can work with STL just fine. Thank you for taking the trouble to make the extra formats available.