SIO2Arduino is an open-source implementation of the Atari SIO device protocol that runs on Arduino hardware. Arduino hardware is open-source and can be assembled by hand or purchased preassembled.

Note: You will need the SdFat library (http://code.google.com/p/sdfatlib/) in your Arduino libraries directory in order to compile.

For more information on SIO2Arduino, see the website at: 
http://www.whizzosoftware.com/sio2arduino

For more information on the Arduino platform, go to:
http://www.arduino.cc