If there's one program of which I'd really like to see the source it would be Reason. And others like Cubase but to a lesser extent. I've done some applications which also do multi-channel audio routing through different processors etc and it's already pretty hard to do that in a nice way, and then some more to make sure everything is fast enough. But that didn't even have such lovely UI on top of it as Reason has.
Yeah I'm with you that something like Reason would be incredibly interesting to see open sourced. I think the fact that they made all of the instruments and effects processors themselves instead of relying on VSTs that would be really interesting to see how they did it, definitely more interesting than Cubase.
