All of us who are running forums as part of our Joomla! sites or have enabled user comments, especially when our user base is relatively local, want to restrict who can access the site in order to reduce spam/hacking attempts. That's what this does, on a country basis using a geo-ip address database.
There are even two modes of operation - external or local. The local option means that you can install the database (free, monthly download from www.maxmind.com) and therefore not be dependent on maxmind's online service being available.
It's early days (I only just installed and tested it) but I would say this is a winner.