Few know that free Linux lurks under Android, and OS/X an iOS have large parts of BSD in them.
Not only that, but the GUI is also FOSS: https://source.android.com/
> OS/X an iOS have large parts of BSD in them.
I think this gives the wrong impression. The interesting parts of macOS and iOS are GUI and drivers, which are proprietary.
The best parts of OSX are brew, iTerm2, and FileMerge.
(Edit in reply to below: Yes, that's my point. brew and iTerm2 are FOSS, FileMerge is part of XCode)
Few know that free Linux lurks under Android, and OS/X an iOS have large parts of BSD in them.