YM2612 Live Player by KStorm is a simple YM2612 controller allows you to create music & noise live on your Megadrive. Functionalities of the YM2612 are all exposed, with the addition of a basic sequencer (keys on/off) and tone generator feature (set mode to 2).
http://www.kstorm.org/index.php/megadrive/29-ym2612-live-player