As photo's, videos, forums etc exist already i'm surprised this wasn't integrated into groups. As in private.
Private photo album in groups
Private video album in groups
Private Events in groups
Ability to add/remove members in a group, i didn't find this function yet incase it does exist.
SO have 3 settings of group type. Public is that anyone can join.
Invite means one needs a invite before they can join by either mail adress or username. Or by moderator wich means one can apply but will not be a member untill moderator approves of the group or admin.
These are rather default features of the more popular systems and definitly one of the things holding oxwall back in gaining popularity. There's alot to learn from other systems oxwall altought they lack the lush interface and look of Oxwall.