RealSpread is a stereoizer.
It stereoizes a mono audio signal or widens a stereo one, without practically compromising mono compatibility.
The spartan GUI conforms to my philosophy of simplicity in plugin design. RealSpread is more effective on single sources, for example a single (mono) Drums Overhead or Room microphone. Of course, you can experiment with stereo sources as well although I wouldn't recommend using it on Groups/ Stems or Masters... except if you are aiming for that something else.
You can insert a Goniometer / Lissajous pattern plugin on the Master bus if you want to observe the effect...