As a condition of Hacksburg's lease, we were required to implement a door-access system using magstripe cards like those issued to students and faculty by the local university (Virginia Tech). This is our fairly simple solution: We have a raspberry pi connected to a relay that opens and closes a strike, and a magstripe reader connected as a keyboard device.
When someone swipes their card, the event is read in, the card data is hashed, and the hash is compared against a list of hashes in an access control file. If the hash is found in the file, the strike opens for ten seconds. If not, nothing happens and a log entry is added.