I suspect this isn't snack-sized (unless someone has old code sitting around to reuse) but I know not where else I could post such an idea.
Basically a Stand Alone program (not a plugin, addon, etc.) that takes the "mono out" (or whatever else audio signal) of the computer and makes pretty patterns.
Most media players have something like this, however websites like
SeeqPod don't.
~Ordstrin