What about Intellicad (https://www.intellicad.org/ )? It seems to be pretty popular among engineers. It reads DWG/DXF (AutoCad format) pretty well. The software itself goes by various names, because Intellicad itself is a consortium. For a nominal fee, you get access to the codebase and can release your own version with your own brand. The thing is shared source, so as a consortium member you need to contribute your changes to the core back to the shared codebase. However this is closed-source.