Hi,
for years I have been playing pipe organ as a simulation (with an organ pedal and 3 keyboards).
I started with Hauptwerk many years ago when it was free.
But the author has decided to "unfree" it. I was very unhappy with his decision.
I cannot recommend Hauptwerk because for what it is, it is way too expensive, so I use some free solutions, mainly GrandOrgue.
In Hauptwerk you need much, much RAM (>8GB) because it has no disc streaming (this is ridiculous for this price).
You can get lots of free, very well-made pipe organs for GrandOrgue or Hauptwerk.
Especially from this side:
https://piotrgrabowski.pl/instruments/
Of course, there are also some professional pipe organs in Kontakt format.
The problem with this format is you cannot really independently pull out the stops.
Old, but not too bad either, there are some free pipe organs in soundfont format:
https://www.realmac.info/jeux1.htm
https://www.hedsound.com/2019/10/hed...soundfont.html
To use a soundfont, you also need a soundfont player, standalone or as a VST.
Soundfont is very, very resource-friendly.
I use mainly virtualMIDISynth which is also a good MIDI GM player:
https://coolsoft.altervista.org/en/virtualmidisynth
best regards
PS: For me the future is/will be Modartt Organteq
https://www.modartt.com/organteq