Voxengo MSED
MSED is a mid/side encoder/decoder plug-in which encodes (splits) the incoming stereo signal into two components: mid/side or, alternatively, mono/stereo pair, and vice versa: decodes mid/side signal pair into stereo signal.
http://www.voxengo.com/freevst/#VoxengoMSEDVST
http://www.baxxy.com/data/VoxengoMSEDVST10.zip