Calf Organ (version 0.0.60 shown above), developed by Krzysztof Foltman of the Calf Plugin team, should probably be considered more of as a synth rather than just an organ. The screenshots above are of Organ's 2 parameter control pages: Tone Generator and Sound Processor. Most of the demos above are of presets included in the installation package. If some demos sound very similar to ZynaddsubFX/Yoshimi, it should be no surprise: some of Calf Organ's waveforms have been sampled directly from Paul Nasca's own padsynth algorithm!
The Tone Generator page offers a faithful layout of nine drawbar tone generators/oscillators, each with its own controls and with a wide selection of waveform options: four sine waves, sawtooth and Ssaw (smooth saw waveshape), triangle, square, pulse (and their respective softened waveshapes), etc. Each oscillator has an FM-style harmonic control knob, and can be panned, phase-shifted, detuned and routed to either amplitude, filter one or filter two.
The Sound Processor page has two filters, the first one with a choice of 12dB-LowPass or 12-dB-HighPass. Cutoff, resonance and key-follow controls are included, and the output can be routed to any of three envelope generators, each with traditional ADSR layout. A global equalization section is also provided here. There are additional interesting control features on this page as well. Aside from the standard global controls such as volume, transpose, polyphony and pitch bend range (provided on the Tone Generator page as well), this page also has a type of FM percussion section, where a carrier sound source and a modulator can be adjusted for harmonics, decay rate, depth and velocity sensitivity. Even if the nine oscillators/drawbars are off, this percussion section will provide interesting timbres that can be considered presets in their own right. Both the carrier and modulator have the same plethora of waveforms to choose from, and the stereo phase knob gives a nice chorus effect. The keyboard layout has a type of x-y-axis with up to four breakpoints, and allows to adjust the timbre response, similar to a traditional key follow function, but with increased capability.
Finally, there is a vibrato section, with wet, amount and rate controls. There are four different vibrato types to choose from, and the output can be routed to various channels such as either filter, or global.
Calf Plugin Website