The top and the bottom section both are buffered 1-in-4 multiples. The input can be inverted with a switch, i.e. its polarity will be changed by 180°. Afterwards four inverted copies are available at the multiples' outputs. Which means you can use these two sections as inverters as well. Bi-polar LEDs display whether the signal is positive or negative: yellow = negative, red = positive.
Center section is a four-input summing stage with amplification factor 1, a so-called unity-gain mixer. The multiples are normalized to the mixer which can be deactivated by patching. If you'd desire to muix four loud audio signals, it might make sense to attenuate them before to prevent distortion.
per multiples: one input, four outputs
Mixer: four inputs, one output
3U Eurorack module, 6HP wide, 25mm deep
current draw: 50mA