Curvessor is a free and open source VST/VST3 audio plug-in that implements a dynamic range processor
in which the response curve of each channel is an automatable spline.

Curvessor can be used as a classic compressor/expander, enjoying the freedom and precision that comes.
with spline editing..

But more specifically, as it allows the authoring of response curves that are not increasing,.
Curvessor can be used for creative dynamic range processing in sound design..