The comment on constraints which still blows me away is the footnote on the readme for Dune 3D:

https://github.com/dune3d/dune3d

>1. I ended up directly using solvespace's solver instead of the suggested wrapper code since it didn't expose all of the features I needed. I also had to patch the solver to make it sufficiently fast for the kinds of equations I was generating by symbolically solving equations where applicable.

(anyone looking for an easy-to-use opensource 3D CAD program should consider it)

For folks not familiar w/ Solvespace it's a light-weight 3D CAD program: https://solvespace.com/index.pl

Probably a bit more approachable for folks is: https://www.cadsketcher.com/ which adds the Solvespace constraint solver to Blender.