Random Music Generator 2 v3
It doesn't sound as great as a real song, but it shows that you can come pretty close to decency by pulling numbers out of a hat within certain constraints.
'Melody length' is rounded to the nearest fourth and determines the number of beats in the melody. 'Harmony instrument' and 'melody instrument' sliders control the instruments used to play the harmony and melody respectively. 'Lower third' and 'tempo' are refreshed after a new melody is generated. 'Lower third' just means that the third note of the scale is lowered a half step, making the sound more minor and interesting. 'Tempo' is the speed of the song.
v3 Added more harmony
v2 Changed lots
v1 Initial release