The Planetarium is a stereo reverb and/or chorus, running into a delay with stereo modulation, running into a compressor with an external sidechain input. It lets you turn any sound into a sea of modulated ambience, then make it pump in time with the music (without the need for a computer or click track).
This video relates to the Planetarium 1 but it gives you a brief idea of what the pedal can do. I’ve since added a few new features in subsequent versions, so the Planetarium 3 can do all this and more. For a better idea of what you can do with the Planetarium 3, see my instagram here: