Erik Sigth has updated shapesynth to include a new finite impulse response pong filter.
Shape is a polyphonic synthesiser allowing the user to draw the shape of the oscillator waveform. The positive side of the oscillation is represented by 32 blocks and the negative side is its mirror, generating all sorts of possible raw retro sounds. Shape is best experienced with Akai SynthStation25 Keyboard Controller.
You can find out more about shapesynth here.