MidiOrg

MidiOrg is a classic organ software emulator. Its architecture is intended to be maximally open, so it shouldn't depend on any specific hardware. The only requirements are at least 1 MIDI keyboard, or MIDI pedal board. Apart from that you can connect it to any source of arbitrary MIDI messages as the handler for stops, couplers, tremulant and jalousies. All these messages are registered visually, without the necessity of knowing them by memory. Because the possibility to use external MIDI controllers is not available to everyone, MidiOrg makes possible to carry out the same actions by switching on/off the visual components on the desktop using mouse or keyboard. For the sound generation, you are supposed to use a soundcard with a fully multi-timbral HW synthesizer (like SB Live! or Audigy).

MidiOrg allows to connect up to 5 MIDI manuals (keyboards) and 1 MIDI pedal board (this restriction is rather practical, theoretical limit is 7 manuals, but this is a pure perversity). Another restriction is the number of stops, by now it is 64 stops.

MidiOrg Home page http://midiorg.wz.cz/en/index.htm

You can download the program and documentation at http://midiorg.wz.cz/en/download.htm

There are several pipe organ soundfonts. The best one to start with is Jeux1.4 by John McCoy. This is available at the Hammersound website. www.hammersound.net.

There is also "Pfeifenorgel", by Andreas Sims Andreas.Sims@t-online.de This sound font costs about thirty-five dollars. There is Bruce Miles English Church Organ sound font. There are also  other soundfonts available for the theater/cinema organ. Many of these soundfonts are available at Hammersound.

Jeux d'orgues 2.1 by Joseph Basquin is another great Sound Font (Have fun, the site is in French)!

This is another program that looks like it has merit, however I have not tried it yet.