I'd like to create a forum for a closed group. Meaning everyone should be allowed to read, but if you want to write you'd need to sign up and a moderator would need to allow your account to write.

So, no anonymous posts, no posts from a newcomer unless a mod allows them to write.

Is this possible with minibb?

1) Make all new registrations require manual approval by your forum's administrator. To achieve this, uncomment the following line in setup_options.php:
//$registerInactiveUsers=TRUE;

(So that the line reads: $registerInactiveUsers=TRUE;)

2) Set your forum(s) to require registration by uncommenting the following line in setup_options.php:
//$allForumsReg=TRUE;

(So that the line reads: $allForumsReg=TRUE;)

All the best -
mb

I suppose this was already discussed few times.

Administrator approving new users?