I'm pretty sure that
http://freerangenaturism.com is public, in the sense that anyone with the URL can read anything that's posted here. But if you want to post anything, as opposed to just reading stuff, you have to be registered and logged in.
Notice that down at the bottom of the screen it'll say something like "7 Guests, 2 Users". Most likely the guests are bots rather than humans, but most of the time I could be one of them, because I usually don't actually log in unless I want to post something (like now).
Stuart and Karla's, by the way.