_Hammond Clones_ are instruments, mostly keyboards or software, which emulate the sound of a HammondOrgan. The main advantage of a clone is its portability compared to an actual Hammond.
Here is a list of some of the available clones.
current and 
discontinued products:# C1 / C2 / C2D # Electro 1 / 2 / 3 / 4D # Stage 1 / 2
Crumar Mojo
Hamichord
KeyB (both single and dual manual models)
MAG Custom Organs (HX3 engine) (several models)
Uhl X3 Smooth (HX3 engine) (single and dual manual models)
StudioLogic Numa Organ / Numa Organ 2
https://www.youtube.com/watch?v=Qd538hiaFAI
Yamaha YC61 Yamaha's first real attempt at a Hammond "clone" with drawbars, waterfall keyboard, etc.
B4000+
HX3 Drawbar Expander
Beatrix - GNU/Linux w/source code(Free, see setBfree below)
v2 Csound instrument (Free)
VB3 (Commercial)
Organ 3 (Commercial)
http://www.soundfonts.it/?a=read&b=13
Pocket Organ C3B3 - Application for iPhone/iPod touch (Commercial)
setBfree - An updated version of Beatrix for more modern GNU/Linux distributions (GPL, Free)
Blue3 - (Commercial)
https://www.ikmultimedia.com/products/hammondb3xipad/ for Mac or PC 
https://www.ikmultimedia.com/products/hammondb3x/ - (Commercial)
Design information.
Keyboard Partner HOAX - Advanced FPGA physical model system, MIDI or keyboard scanner in, Leslie simulator, presets, etc. Blank PCBs to fully assembled boards.  No source code or PCB etch patterns.
Prop B3 - Parallax Propeller microcontroller project with MIDI in, percussion, chorus/vibrato, reverb, Leslie simulator, foldback, keyclick, overdrive, etc.  No kit or pre-etched PCB available.
Aurduino Roto - Incomplete physical model by Peter Teichman using Arduino and ?MidiVox.  
More information.Most of these organs are not, strictly speaking, "clones" but they all have electromechanical tone generators. Like the Hammond, these organs rely on motors, gears, and in some cases, belts to turn "tonewheels".
Telharmonium - Thaddeus Cahill's instrument was certainly the first electromagnetic organ (1897).  Gigantic generators were needed in an era BEFORE amplifiers and loudspeakers.
More information.
Robb Wave Organ - A very limited production electromagnetic organ invented by Morse Robb (1936).  Like the Compton, produced complex pipe-like waveforms.
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