While not a compressor, most people searching for "C6 Stereo" actually just want to make their track wider. iZotope’s Ozone Imager is the industry standard.
If you use a DAW that supports "Plugin Racks" or "Effect Chains" (like FL Studio Patcher, Ableton Audio Effect Rack, or Reaper FX Chains), you can combine the free plugins above to create a super-C6. C6 Stereo Vst Free Download
This is the closest you will get to the C6 experience without paying. TDR Nova is a and multiband compressor. While not a compressor, most people searching for