The Brainworx bx_digital V3 is a 11-band equalizer that has become synonymous with the term "M/S processing." While most equalizers process the Left and Right channels of a stereo file, the bx_digital V3 processes the Mid (center) and Side (stereo edges) information.
If you don't want to deal with trials or subscriptions, here are three totally free VST plugins that mimic aspects of bx_digital V3. Brainworx Bx-digital V3 Free Download