If it's for 2D I like librecad.. I can't get my mind wrapped around freecad.. If it's 3D, you can get surprisingly far with just sweet home 3D, or even blender (you can do accurate enough things with blender if you decide what a square is, and snap to grid)

Note for Blender there is:

https://www.cadsketcher.com/

That said, if you want 3D CAD, the simplest option is probably:

https://dune3d.org/