This kind of relates to [Server Fault close reason text](https://meta.stackoverflow.com/questions/272020/server-fault-close-reason-text) but in a direct and global way:

What's the difference between these sister websites [(1)](https://networkengineering.stackexchange.com/help/on-topic) [(2}](https://serverfault.com/help/on-topic)?

In my opinion, they might not be unique enough for most people to know which one to choose.