DragonFlyBSD

On an ufs partition, rmdir(1) removes only empty directories.

If one uses it on a hammer filesystem, it is also able to delete regular
files:

Ufs example:

$ touch one two
$ mkdir three
$ rmdir one two three
rmdir: one: Not a directory
rmdir: two: Not a directory
$ ls one two three
ls: three: No such file or directory
one two

Hammer example:

$ touch one two
$ mkdir three
$ rmdir one two three
$ ls one two three
ls: one: No such file or directory
ls: three: No such file or directory
ls: two: No such file or directory