I did a Yamaha RY-30 sound editor, I even added randomise functions. The XG tools. An AHI output tool for B&P and tools to control the Delfina DSP software from within B&P (you could automate EQ changes and so on). I also did a MIDI output tool for B&P which let you use any 3rd party serial card for MIDI.
Getting a programming job totally kills your enthusiasm for writing code though lol.