Ripples, from Mutable Instruments, is a classic analog filter. It has 4 individual outputs, providing both two-pole and four-pole architectures, which gives a -12dB (2-pole) or a -24dB filter slope (4-pole). It has resonance that can self-oscillate, producing an extremely clean sine wave. Another aspect of Ripples that improves on historical designs is its implementation of loudness compensation. This makes sure the lower frequencies don't lose volumes when resonance is increased, something common in virtually all vintage synthesizers. Also built in is a VCA, making Ripples a perfect final module in a subtractive synthesis patch.
Frequency CV 1 (1V/Oct)
Resonance CV. Self oscillation starts at 4V. Control voltages above 5V are non-linearly compressed, for fine control of resonance overdrive
Frequency CV 2 (with bipolar attenuator, from -1V/Oct to 1V/Oct)
VCA level. Control voltages above 5V are non-linearly compressed.