Sverchok
From Wiki.OSArch
Sverchok is a parametric tool for architects and designers for Blender. You can use it to program objects' shapes without knowing any programming languages. Sverchok has been inspired by Grasshopper from Rhino 3D and it uses a similar node-based visual programming principle. We are trying to bring this feature set to Blender users.
Sverchok nodes allows us to model geometry with nodetrees. Read the full Sverchok documentation
Sverchok is a Blender addon and also works well with FreeCAD