This is a stripped-down version of the 23b hackerspace's Open Access Control system, intended for embedded use with an RFID reader and Ethernet shield for authenticating Wiegand RFID cards with a webservice. Please see http://code.google.com/p/open-access-control/ for the main/full version.
For more info, contact @willbradley on Twitter.
Structure
This folder
Open Access Control folder
Open Access Control.pde (Arduino code -- open from the Arduino IDE.)
libraries folder (copy the contents of this folder to your Arduino program's libraries folder.)