Some hackers have has wired up an Atari 2600 emulator to Max/MSP/Jitter, ending up with a virtual Atari 2600 whose circuitry can be manipulated in lots of ways, creating weird and nifty visual effects:
The pixels rendered by the Atari 2600 emulator can now be treated as matrix data by Jitter. So, the game screen can be moved about in 3D space, stretched, and mapped to various types of surfaces (a sphere, for example).
Embedded within the Max/MSP programming environment, these manipulation parameters can be changed in relation to a signal, directly tied to music played through MSP.
It also means that a nearly unlimited number of manipulations can be done at the emulation level. Memory accesses can be visualized (including both RAM and ROM), colors manipulated, and synchronization signals tweaked.Of course, it is only usable if you have Max/MSP and Jitter (which cost a lot of money); though perhaps someone will do something like this for Pd?