[graemep]

Average/most popular distros, maybe.

The full range of distros are very different from each other. Consider Void, Alpine, Gentoo, Chimera, NixOS.....

Different C libraries, init systems, different default command line utilities....

[anthk]

That's nothing. Alpine can run Glibc binaries with compat libraries.

Try running a FreeBSD binary under OpenBSD.

[graemep]

But only with compat libraries. Similarly FreeBSD can provide Linux compatility. Wine lets you run Windows binaries on multiple OSes.

[anthk]

You can't run neither FreeBSD nor NetBSD binaries under OpenBSD.