This video, via Flux302 of Fluxwithit.com, takes a look at the STG/Soundlabs Mankato filter for Eurorack modular synthesizers.
The Mankato Filter is a four-pole lowpass filter with positive and negative outputs at every pole, giving you slopes of 6 dB/oct, 12 dB/oct, 18 dB/oct, and 24 dB/oct simultaneously.
The negative slope outputs allow you to use the Mankato as a quadrature sine oscillator with 8 available phases. The Mankato will self-resonate from subaudio to superaudio, and responds to one volt per octave through its unattenuated control inputs.
The signal inputs are DC coupled, which allows you to use the Mankato as a voltage-controlled slew limiter.
The Mankato Filter is based on a PCB sold by Magic Smoke Electronics of a circuit designed by Thomas Henry. See the STG site for details.
Sounds tasty!
I think it bears mentioning that this is filter is a DIY project, first and foremost. STG has obviously done an excellent job, but anybody with some electronics experience and patience should be able to buy a PCB for $20, components for another $20-30, and put this together themselves. http://magsmoke.com/TH-201-Mankato-Filter-VCF.asp
(Yes, you still need to buy or make a front panel)