CAD/CAM constraint-based geometry sketcher for Blender

Article note: It's sort of shocking how much of a hard problem generalized parametric CAD is, both in the algorithmic and user perspective. The SolveSpace+Blender arrangement here actually seems reasonably pleasant. Also, from the comments, I didn't realize the commercial offerings were almost all front-ends to the same set of kernels, D-Cubed 2D DCM for 2D constraint solving, and either Parasolid or ACIS (or, for Autodesk, a fork of an old version of ACIS) for the geometric kernel. A couple of the small and/or open source players are using different parts, but the big players are basically hyper-specialized chrome.