Yeah, Lounge was intended as off-topic, but also for things that don’t fit elsewhere.
If there’s an accumulation of topics of one kind that aren’t off-topic, we can always make a new category for them.
Changed default. Everyone can see it.
Scrapyard was intended as a place for failed projects, prototypes, broken things and finding out things that don’t work. Like my own project or Pierres.
Ideas can go where they fit. Engineering related ideas into Engineering, etc.
Engineering analysis can happen in Engineering or Engineering - System Design if it applies.