[gosubpl]

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.

[specialist]

Thanks. That looks bitchin. Will check it out.

Looking at its stock UI, I'm reminded of one of my basic grievances with CADD of the AutoCAD model:

I hate layers.

When doing architectural plans, which layer does the electric water heater go onto? 'ELECT', 'PLUMB', or a special case 'ELECT-PLUMB'?

Much better would be something set based. (Today we'd probably call them tags.) Instead of toggling visibility, views should be queries.