OpenBSD does support some older hardware already not supported by, say, most Linux distributions. As an example MacPPC has’t had support from most Linux distributors since IBM Power went little-endian, but OpenBSD runs fine on it.

NetBSD is, however, the gold standard for an OS that runs on just about anything. Their (maybe unofficial) slogan has been “Of course it runs NetBSD!”. Their logo has a flag in it because they “plant their flag” on so many platforms.

https://wiki.netbsd.org/ports/