FreeCad
Beside Blender there is FreeCad.
FreeCad is a free software developed by two German engineers witch is not production ready yet, but could become a very solid basis for open source architecture software. It's based on the OpenCascade technologies,the inventor language, coin3D, pivy and Qt.
FreeCad is aimed to be a fully parametric CAD like SolidWorks, Catia or Revit.
FeeCad as a Library
FreeCad can be use as an external Library. Potentially, it will be possible from Blender and through Python, to have access to all FreeCad functionalities such as parametric and drawing functions.
Draft Module
Yorik Van Havre, a blender user and freelance architect based in Brazil is developing a 2D draft module that will soon be a future alternative to Autocad © for 2D drawings.
Yorik did a great work and did already implemented some core tools :
- dxf import/export
- snapping
- ortho-constraints
- line
- polyline
- arc
- circle
- text
- rectangle
- move, scale , rotate
- offset
- and magical join | explode | boolean function !