TrollBridge is a set of Python scripts and iptable configuration that allows you to capture unknown network clients and authenticate them before allowing them to access the network (local, internet, 802.11 WiFi, etc.). It is based on the firewall script from NoCatSplash, but is written in Python instead of 'c'.
It can be used to to setup a network hot-spot for your business, school or home. The only authorization methods currently available are a skeleton username/password example, and an example using iButton devices. When a unknown MAC addresses tries to make a connection to the protected network the iptables rules redirect any access (web or otherwise) to port 5280 where the Apache server then displays the authentication page. Yes, MAC addresses are used to keep track of authorized users, so this system is susceptible to MAC spoofing.
The scripts are not 'plug and play', you will need to customize them for your unique situation, as well as modify your iptables settings and add a virtual host to the Apache web server.