It may not be open source, but DraftSight is free to use (commercial use included) and has 99% of the functionality of autoCAD for 2D stuff, but its a bit anemic if you are doing 3D.

I use it all the time at work, very easy to pick up if you are used to autoCAD (similar interface).

https://www.3ds.com/products-services/draftsight-cad-softwar...