Specter is a VST effect for Windows. It was developed for mastering but is very useful on single instruments, groups or effects. The main goal was to make it "transparent".
The main difference from other similar effects is that the input signal isn't split in bands. The plug-in continuously calculates a single response including all the modules and applies it to the input signal, thus avoiding artefacts coming from several effects in series and phase artefacts.
There are 4 inputs and 2 outputs, allowing mono and stereo sidechain (depending on the host).
Pricing and Availability:
Price: 279 euro.
(VAT or regional taxes could apply)