The Modor NF-1 has been a very popular synth, we really enjoyed it when we got one for review some time back... The Comb Filter prototype that we saw at this years Superbooth is a stereo eurorack version from the NF-1.
Comb filters are implemented by adding a delayed version of a signal to itself, causing constructive and destructive interference. The frequency response of a comb filter consists of a series of regularly spaced notches, giving the appearance of a comb. You can get a number of different effects from a Comb filter and it not something that you see very often in the eurorack world.
More info at Modor Music