CAD Sketcher is a brand new add-on for Blender that adds 2D sketch driven CAD functionality. The project is commercially free, as well as open source under the same GPL v3 open source license as Blender. CAD Sketcher is described as:
Constraint-based sketcher addon for Blender that allows to create precise 2d shapes by defining a set of geometric constraints like tangent, distance, angle, equal and more. Sketches stay editable and support a fully non-destructive workflow.
Getting started is easy enough, just install this add-on (direct zip link), then once enabled in the add-on settings, install the Solver Module. Note, if this process fails, you need to make sure you have a new version of Python installed. On both tested Windows machine, this step was required, while on MacOS it was not.
This add-on is still in the early stages and the developer is looking for feedback.
You can learn more about CAD Sketcher and see it in action in the video below.