The firmware for the Arduino Uno can be found in the SVN Repository.
As the Holoseat only controls locomotion, you will need to use a keyboard or a controller for other inputs. One of the Holoseat developers prefers to play games on a recumbent exercise bike, and in turn uses a controller. For PC games, he uses JoyToKey to map an XBox 360 Wired controller to keystrokes. Below are the configuration files for the games he has played using the Holoseat.