[waddlesplash]

OpenBSD is itself a fork of FreeBSD from many years ago, and while there has been a significant amount of API divergence, the differences are not as large as you might first expect. The "OpenBSD compatibility layer" is just a bunch of headers which add more or differing functions from FreeBSD, it does not have any .c files. It works just fine.

[chungy]

OpenBSD was actually a fork of NetBSD ca. 1996; NetBSD and FreeBSD in turn are basically sibling-forks from 386BSD.

[waddlesplash]

Ah right, seems I got the BSD lineages mixed up. Well, the basic point still stands, anyway.