BRL-CAD
I once worked as a developer for Pro&#x2F;Engineer, and sometime after that, I was on the user side using BRL-CAD. I can&#x27;t speak to the quality of the product these days, but at the time, BRL-CAD was achingly slow and riddled with bugs. Using it for my day-to-day work made me want to quit my job, and I left as soon as I had something more promising lined up. I am sorry to sound like I&#x27;m unfairly judging BRL-CAD. Perhaps we were using it for something it was not intended to do, or not the way it was meant to be used. I knew my way around the Pro&#x2F;E interface and it was miles ahead of BRL-CAD. But even CADDS-IV was better than BRL-CAD. I can only speculate that being government-funded, the dev team for BRL-CAD had to make brutal decisions regarding when the feature set was &quot;good enough,&quot; because they were working with a very limited budget tied to specific program goals. I don&#x27;t know. I do know that using BRL-CAD was hellish back in the day.