By default, UNA has Privacy engine which allows a member to limit his content's visibility to some group of people (visitors, common members, etc). But sometimes it's needed to block only one or more undesirable members.
The Black Lists app adds this Very important feature to your UNA based site. Your users would be able to block undesirable member(s). Blocked member cannot view a content (posts, polls, ptoducts, etc.) of blocking member.