Radium Compressor is the system compressor in Radium,
but distributed as a standalone jack application.
Radium Compressor uses the stereo compressor found in
effect.lib in the Faust distribution.
This compressor is written by Julius O. Smith III.
The GUI shows accurately the sound used for compression,
and how much the sound is being compressed.
I haven't seen this in any audio compressor GUI before,
but it's probably been done before.
Demonstration video:
http://www.youtube.com/watch?v=KphCxloBq2w
Tar-ball:
http://archive.notam02.no/arkiv/src/?C=M;O=D
Source repository:
https://github.com/kmatheussen/radium_compressor