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.