ACL - M/S Matrix
With just eight connections and four knobs, M/S Matrix is an exceedingly simple yet exceptionally useful module. Quite simply it can simultaneously extract the mid and side signals from a stereo input whilst combining a MID and SIDE signal to form a stereo signal.
There are probably way too many handy applications for this device to cover them all... but let's give it a try anyway.
At the most basic, without any additional processing, the module can be used to control the width of an incoming stereo signal. Moving up the sophistication ladder, by inserting a filter into the SIDE signal path and filtering out low end information, you could use it to mono the bass element of a stereo, which can be useful for everything from mastering a track for vinyl to ensuring your bass doesn't suffer from phase cancellation on less than perfect sound systems.
On a similar note, you could apply compression to either the MID or SIDE signal path, thickening it up and raising its perceived level. Or you could pump one of them (or both at different amounts) with sidechain compression. Or saturate one. Or brighten them with EQ. Or you might use the module as a mixer, attenuator, subtractor, inverter... or absolutely anything you want - which is both a sneaky way to cover all the possible applications after all, and a nice way to end this product description.