Kneader is a crossover filter with two fx loops, one for bass frequencies and the other for high frequencies.

You can connect other pedals to the chain and make them work only for the low or the high frequencies (e.g. bass guitar with clean lows and distorted highs).

It gives you control over the crossover frequency, volume of the low and high return signals and phase of the two bands.

Really useful for bass and guitar (but especially for bass)