It's a stereo widening tool, which essentially uses a ton of allpass filters to let you place elements in the mix. Each channel has a distance (number of allpass filters), a cutoff frequency and a resonance (width of cutoff) parameter. You can also change it from L/R to M/S mode and there's a button that helps with checking for mono compatibility.
Here's a little intro video: https://youtu.be/6Wrzmq6bmyg