Part of BeOS conforms to POSIX (probably an older edition). Would any question on certain aspect of BeOS be on-topic here?
I think the same rules we apply for macOS and Android could apply to BeOS:
- The Unix foundation underlying OS X (but generally not frontend application questions)
- The underlying *nix OS on an embedded system or handheld device (e.g. an Android phone)
The conforming parts would be on-topic, the more exotic parts wouldn't be.
(It might be completely on topic on Retrocomputing, but a quick search didn't show (m)any questions about BeOS specifically.)