You may want to run a forum to discuss with friends, and not have everything out in the open. With Flarum, that is actually surprisingly easy.
First, create accounts for all your friends/members.
Then, go to Flarum > Administration and change the permission for "view discussions" to "members only".
Change "Signup" to "Closed". You will have to add new members manually.
Occassional visitors will now see an empty forum. You can verify that with your browser in Incognito mode (Chrome: control-shift-N).