I had most success with DeltaCAD. Unfortunately it's only for windows and now also discontinued.

I also like CadZinho (https://github.com/zecruel/CadZinho) but it's missing some features (chamfers and fillets) and it's not that easy to draw precisely sized lines in it.

FWIW, CadZinho (and a bunch of other programs) are listed at:

https://old.reddit.com/r/shapeoko/wiki/cad

(which badly needs to be cleaned up and re-formatted)