Matthieu Brucher has released ATKSidechainCompressor, a free dual channel compressor with side chain plugin for Windows and Mac.
I’m happy to announce the release of a side-chain stereo compressor based on the Audio Toolkit. It is available on Windows and OS X (min. 10.8) in different formats.
This stereo compressor can work on two channels, left/right or middle/side, possibly in linked mode (only one set of parameters), and can be set up to mix the input signal with the compressed signal (serial/parallel compression). The side chain channels can be used to steer the gain stage (the same setup will be used, right/left or middle/side).
ATKSidechainCompressor is available as free download for Windows and Mac (VST/ AU).