The WiFi Guard Dog project is a complete and embeddable captive portal solution for wireless community groups or individuals who wish to open a free HotSpot while still preventing abuse of their Internet connection.
The project's homepage is: http://dev.wifidog.org/
Mailing list interface: http://listes.ilesansfil.org/cgi-bin/mailman/listinfo/wifidog
The project's software is released under the GPL license and is copyright it's respective owners.