For NaOpGenMo 2014 I wrote a program, named bba.c, which generates an opera.
It can actually generate many operas, but here is the 2-hours-and-39-minute opera it generates with random seed '0', featuring the "New Jersey Piranha" against the "Omaha Incubi".
At the moment the music is only available as General MIDI files. Possibly some day this will change.
Yes, there is a lot of nonsense (aka bugs) in the Bass lyrics. That was the last part of the code I wrote before the deadline and I didn't have time to test it.