My understanding (potentially faulty) is that OS X is a fork of FreeBSD. While FreeBSD and Linux are both "UNIX-like" operating systems, they have a different core.
I thought the OS X kernel was based on Mach or something. A number of the userland utilities were taken from FreeBSD. IIRC there is some OpenBSD code in there too. OS X is a UNIX as they paid for the certification. FreeBSD is also a UNIX, but they can't state that as they never paid for the certification & likely never will.
Linux is not UNIX, but certainly UNIX-like.
OS X is not a direct
fork of FreeBSD (Or whichever BSD it uses). Yes, it uses BSD code, but it also has Mach code. The truth is that OS X's kernel is called XNU, or X is Not Unix. It was probably named such when OS X was a UNIX-like but not officially certified to be called UNIX (It has since passed verification). Here
is a YouTube link to an old talk about the Mac OS X kernel (pre-10.6, which did introduce a true 64-bit kernel).
What will stop you from running Avernum 1 on modern x86-based Linux distros are threefold: 1): Different
binary formats (OS X/Darwin uses mach-o, although Avernum 1 would be a Carbon CFM application, so double whammy there), 2) different APIs (Carbon/QuickDraw aren't available), and 3) different CPU architecture (Avernum 1 was written for the PowerPC as opposed to Intel's x86. There are quite a few differences between them, not least of all is endianness *shudder
* Just porting Big Endian code to Little Endian is a pain!).
Yeah, Wine is the way to go. Linux may not be UNIX-certified, but it's probably the most well-known derivative. TL;DR This YouTube link
describes the Mac OS X kernel is great detail.