Developed by V3Sound in collaboration with Symphonia Concert Library, and running in the supplied Best Service Engine instrument (VST/AU/standalone), Organum Venezia is a sampled pipe organ "recorded near Venice, Italy".
There's not much to the interface - just 18 buttons for activating a range of single stops and combinations, and sliders for volume and convolution reverb depth - and being a pipe organ, there's only one velocity layer, of course, which explains the tiny 330MB footprint.
For that full-on organ sound, all you have to do is activate the Tutti button, which combines all stops, and sounds suitably majestic. For custom tones, the individual stops - Trumpet 8, Flute 4, 8 and 16, Prestant 4, Celeste, etc - serve as a small library of stackable layers, while the Combis comprise various combinations of stops, some of which aren't available singly.
The pipe organ is all about power, and Organum Venezia certainly has plenty of that.